In this last post we covered replacing a cars piston rings. But, in this post we’ll run through replacing a head gasket.
Why? Because, to replace piston rings, you need to remove the cylinder head.
But, to access the cylinder head, you must first remove the “cylinder head gasket”.

The car I carried out the repair on was a 2014 Mazda Cx-5 SkyActive 2.2 Diesel.
And while it made sense to only “briefly” touch on this topic in the last post. It lined up the perfect opportunity to cover head gaskets, in full detail today.
So here’s what we’ll cover.

Can a car still drive with a Failed head Gasket?
The short answer is YES! Some cars will, and most certainly still can, but should never be, driven with a blown head gasket. Although, how the car will drive, is likely with many faults.
So never rule out the possibility of a head gasket failure because a car can “technically drive”. As it simply depends on, where?, and how?, the gasket has blown.
That being said, if you suspect a head gasket to be the issue. Then immediately stop the car, call a recovery service, and prevent the possibility of further damage being caused to the engine.
However, “suspecting” without testing will never suffice. Which is why professionals follow a precise process when diagnosing the symptoms of a failed head gasket.
Once the diagnosis has confirmed that a head gasket is the issue, you can then begin to remove the components preventing access to the problem area.
Please Read!
The following section specifically helps with diagnosing a failed head gasket.
However, if you’re already certain that the gasket is blown, then you can skip ahead to start making the repair.

How to Accurately Diagnose a failed Head Gasket
A failed head gasket can be found in a in a number of ways. Which is down to the fact that ‘the gasket can blow in a number of ways’.
A few of these ways include; general wear, overheating, loose head bolts, turbo over-boosting, faulty thermostats, pre-ignition or detonation, etc.
However, the method used for testing should always be determined by current symptoms. Because, how you would approach overheating situation is totally different to the approach you would take for a non starting engine.
And in some cases, you might see no symptoms. Which is why it’s paramount to carry out thorough testing before starting repairs.
Visual examples: Causes & Symptoms of head gasket Failure
The following images will provide examples of the types of symptoms that each failure can present.
Understanding this will help you to decide on the appropriate test to carry out before starting the repair.





Fault Diagnosis: Understanding the symptoms
The table below consists of the most common symptoms of a head gasket failure.
Each section will additionally provide the suggested checks that can be made to identify how and where the gasket has blown.
- Excessive exhaust smoke
- Milky light brown Engine oil
- Bubbling coolant in reservoir
- Loss of Coolant or oil (with No Visible Leaks)
- Visible engine oil or coolant leaks
- Engine Missfire
- Engine Overheating
- No In Car Heating
- Low Engine Compression
- Check Engine Light (on dashboard)
- Visible Steam from Under the Hood
- Sweet smell coming from Exhaust
Reason
Coolant or oil is entering the engines combustion chamber and being burned
How To Identify Fault
Visually inspect exhaust smoke with engine running
Other Possible Causes
Faulty turbocharger, damaged piston rings, bad valve seals, or damaged cylinder walls
Reason
Gasket has blown between oil and water jacket passages in the engine
How To Identify Fault
Remove engine oil filler cap and inspect
Other Possible Causes
Build up of condensation in engine, cracked engine block, or oil cooler failure
Reason
Gasket has blown between combustion chamber and coolant jacket in engine. Combustion gases are entering the coolant system.
How To Identify Fault
Inspect coolant in reservoir while engine is running
Other Possible Causes
Air trapped in cooling system, clogged radiator, or faulty radiator cap
Reason
Oil or coolant is being burned in the engine, dissipating without leaks
How To Identify Fault
Run engine an inspect exhaust gases for unusual smells or smoke
Other Possible Causes
Evaporating coolant from a hot engine, small undetected leaks in hoses or radiator
Reason
Gasket has blown between oil or coolant passage and edge of the engines mating surface
How To Identify Fault
Inspect the engine and ground for visible signs of leaks
Other Possible Causes
Cracked oil pan, loose oil filter, or damaged hoses
Reason
One or more cylinders in the engine is not operating correctly
How To Identify Fault
Listen for rough idle, unusual engine sounds, or run diagnostic scan
Other Possible Causes
Faulty spark plug(s), ignition coil(s), or bad fuel injector(s)
Reason
Coolant loss or air pockets preventing heater core from receiving hot coolant
How To Identify Fault
Check if the heater blows cold air even with the engine at operating temperature
Other Possible Causes
Faulty thermostat, radiator, or water pump
Reason
Gasket is blown between the combustion chamber and the coolant passages.
How To Identify Fault
Check if in car heating blows cold while engine is at operating temperature (roughly 90°)
Other Possible Causes
Faulty heater core, stuck thermostat, or clogged heater hoses
Reason
Gasket has failed between cylinders resulting in a loss of pressure
How To Identify Fault
Perform a compression test with a gauge
Other Possible Causes
Faulty piston rings, cylinder walls, valves, or fuel injector clamp. Or engine is cracked
Reason
Engine ECU has detected a fault in one or more cylinders. May result in limp mode
How To Identify Fault
Run diagnostics test with OBD scanner
Other Possible Causes
O2 sensor failure, mass airflow sensor issue, catalytic converter problems, turbo failure
Reason
Coolant is entering the engines combustion chamber and being burned
How To Identify Fault
Start engine. Then, open oil filler cap to confirm steam is coming from inside the engine
Other Possible Causes
Radiator or hose leak, or faulty thermostat
Reason
Coolant is mixing in combustion chamber and being burned
How To Identify Fault
Stand behind car with engine running and smell
Other Possible Causes
Leaking coolant hoses, faulty radiator, or faulty heater core
Tests you can run to Confirm the gasket is blown
The following table contains a list of the tests that can be carried out to identify the type of failure the engine has.
Additionally, you should now be able to read the symptoms and determine the appropriate test that should be carried out to confirm the fault.
Test Name | Test Description | Time To Carry Out | Experience Level | Process | Video Link |
---|---|---|---|---|---|
Chemical Block Tester | Detects if there is exhaust gases in the coolant system | 15 minutes | Beginner | Fill test tube with solution. attach to coolant reservoir. Start car. Squeeze test pump. Check if solution changes colour. | Watch here |
Compression Test | Measures the level of compression being generated in cylinder(s) | 30–60 minutes | Intermediate level | Remove spark or glow plugs. Mount test hose with gauge. Crank engine and take results. | Watch here |
Leak-Down Test | Identifies if there are leaks or a loss of pressure in cylinder(s) | 45–90 minutes | Professional level | Mount tester to spark or glow plug hole. Increase air supply (100 PSI), then check gauge for leaks. | Watch here |
Coolant Pressure Test | Identifies leaks in the cooling system | 20–30 minutes | Beginner level | Attach tester to coolant reservoir, then pump to 15 PSI. Check gauge and hoses for leaks. | Watch here |
Oil Analysis | Detects contamination of oil with coolant | 5–10 minutes (sample collection); lab testing: 2–3 days | Beginner level | Extract about 50ml of oil from engine. Send sample to lab for analysis. | Watch here |
Exhaust Gas Analyser | Identifies if exhaust gas (e.g., CO2) is entering the coolant system | 20–30 minutes | Professional level | Attach tester to exhaust, then read on screen data. | Watch here |
Visual Inspection | Identifies visible signs of leaks, contamination, or wear in the engine and coolant system | 15–30 minutes | Beginner level | Visually inspect in and around the vehicle | N/a |
Chemical Dye Test (UV Dye Test) | Detects external leaks in the coolant system | 30–60 minutes | Intermediate level | Add solution to coolant reservoir. Run engine for 15 mins. Inspect with UV light for leaks. | Watch here |
Boiling Coolant Test | Identifies overheating issues via the cooling system | 15–20 minutes | Beginner level | Run engine to normal operating temperature. Then inspect coolant in reservoir | Watch here |
Infrared Thermography (Thermal Imaging) | Identifies abnormal temperatures in particular areas of the engine | 30–45 minutes | Professional level | Use thermal camera with engine running to see hotspots on engine. | Watch Here |
Vacuum Leak Test | Measures fluctuations in vacuum pressure, indicating a loss of compression. | 20–30 minutes | Professional level | Attach a vacuum gauge problem area, then pump, and check gauge. | Watch here |
Road Test | Identifies unusual engine performance | 10–30 minutes | Beginner level | Drive car uphill, at high speed, under high load. Review performance. | N/a |

A Step-by-Step Guide to Replace the Head Gasket On A Car
The following sections in this post will provide you with a comprehensive guide on:
- Removing the cylinder head and its associated
- Correctly cleaning the engine
- Inspecting the engine and other relevant components
- Replacing the head gasket
- Reassembling the engine
- Then, Testing the engine once the repair is complete
Lets get started.
Tools Checklist
“A mechanic with no tools is like a fish with no water”.
So, here’s a list of tools that you will need to replace a head gasket.
Basic Tools
- Basic Screwdriver set
- Rubber Mallet (to free up the cylinder block when removing)
- Basic ratchet and socket set (socket sizes ranging 8mm to 21mm)
- A long Pry Bar
- Car Jack
- Axle Stands
- Liquid Paint Marker (for marking timing chain)
- Engine Degreaser (and a rag)
- Acetone (small bottle of nail varnish)
Special tools
Here’s a list of specialised tools which are not those that you’ll find a regular toolbox
- Torque Wrench (try this adapter)
- Mapp Blow Torch
- Thread Chaser Kit
- Feeler Gauge
- Piston ring grinding tool
- Crankshaft Pulley Holding Tool
- A Mechanics Precision Straight Edge Tool
Tools that You “might” need
- Wynn’s Instant Silicone Gasket
- Timing Chain locking tool
Non-essential (Highly Helpful) tools
While it’s certainly possible to complete this repair without the following tools, I’d still highly suggest to have them.
An impact wrench will make easy work of seized bolts, and a breaker bar will increase leverage, improve control, and enhance accuracy.
- Torque Angle Tool
- Impact Driver (Check out Dewalt)
- 1/2 inch Breaker Bar (link to Amazon listing)
- Electrical clip separator tool (link to Amazon listing)

First things first.
Disconnect the battery, then drain the fluids. This consists of draining the coolant, and draining all engine oils.
Once that’s done, its time to tackle the cylinder head, timing cover, and valve cover.
disassembling An Engine – The Simple Way
I try to simplify engineering. So thats exactly how I teach it.
To date, all the engines I have come across have been built on the same fundamental foundations.
On the bottom end, is the engine block (containing the crankshaft and pistons). On the top end, is the cylinder head (containing the camshafts and valves).
In the middle, is a head gasket, which is sandwiched between the two, to provide an air tight seal. While a timing chain, joins the top and bottom components.
To breath in (i.e., get air), the engine has a air intake system (usually mounted to the front). And, to breath out, there is an exhaust system (usually mounted to the rear).
A turbocharger or supercharger is in other words, an “enhancer”. That works by “enhancing” the already existing applications taking place in the engine.
And while some engines feature two cylinder heads. They are almost always built on the same foundations.
Now you understand engines. The simple way.
It’s time to begin disassembling…
Remove The Valve Cover
As the valve cover is the first point of call, that’s exactly where we’ll start.
- Remove the engine cover
- Remove all components in air intake system (i.e., air filter, and air intake ducts)
- Remove coolant hoses and any hose connected to valve cover
- Unclip wiring looms connected to the cylinder head, injectors, and surrounding area
- Remove fuel rail, fuel injectors (and high pressure fuel pump if you have one)
- Remove supercharger (if you have one)
- Remove the valve cover
Remove the Timing Cover
In almost all instances, the timing cover must be removed to access the cylinder head.
That being said, the steps to follow for most vehicles consists of:
- Jack up the front end of the car
- Place axle stands beneath the vehicle
- Remove both front wheels
- Remove the crankshaft pulley bolt (then remove pulley)
- Remove any other component preventing access to timing covers bolts
- Remove the timing cover bolts (then remove timing cover)
Some turbo or supercharged cars will unfortunately contain additional steps here.
Subject to the engines design, you may need to additionally:
- Remove the front chassis (which can be around 30 mins alone as a DIY project)
- Remove the downpipe (i.e., the DPF on diesel cars)
- Remove the turbo
Once this is done. Its time to move onto the cylinder head.
Accessing The Cylinder Head Bolts
You should now be able to see the engines camshafts, timing chain, rocker arms and cylinder head bolts.
The next steps are to:
- Wrap a flathead screwdriver in a small rag then use it to push back on one of the timing chain guide
- Lock the timing chain tensioner in position with a locking pin (or any metal pin you can find)
- Use a liquid marker pen to mark three points where the timing chain meets the camshaft gear.
- Lock the camshafts if necessary for the engine type
- Mark three points where the timing chain meets the crankshaft gear (this will help you to understand where it needs to go back)
- Remove the timing chain
- Remove the camshaft journal bolts (then remove the camshafts)
- Remove the rocker arms making sure they are placed in exactly the same places along side the associated journals. Then store in a place where they will not be moved
- Remove the timing chain guides (if necessary)
- Loosen each hold bolt about 90° starting from the outside bolts near to the extreme edges and then working your way in to the centre.
- Fully loosen all of the cylinder head bolts by following the same sequence
Once bolts in the cylinder head have been removed, its then time to:
- Lift the cylinder head up and away from the engine block.
Note that this may take a little wiggling around. So its best to best to keep a rubber mallet handy to help you free the head from engine block.

Cleaning the engine (And Associated Parts)
Tools you’ll need:
- Engine degreaser (or brake cleaner)
- Acetone (i.e., nail varnish remover)
- Thread Chasing Kit
- Engine oil (the required oil for the engine)
- Plastic or brass scraper
- Compressed Air (if possible)
Hands down, the best engine degreaser I’ve used to date is STP’s Engine Degreaser. But theres one major gripe that I have with it..
There is simply never enough of it!
The large can comes at 500ml, which is extremely effective on small areas. However, to cover larger areas, such as the entire engine, it’s most cost effective to opt for their multipack option.
Additionally, you can also pressure wash non delicate components (on a low setting). Then use a bristle brush and hand scraper (or ultrasonic cleaner) to clean up the remaining parts.
A good backup to keep is a 5L bottle of Gunk, as it’s an extremely effective product that works well on a variety of vehicles. And while it’s not as penetrative as the STP solution; it will certainly in every case, last for a much longer time.

Clean the Cylinder bolt holes (In The engine block)
Use compressed air (if possible) to blow out loose dirt and debris from the head bolt holes. Alternatively, wrapping a clean rag around a flathead screwdriver, then feeding it down into the hole will also work just fine.
Just make sure to be careful when using the latter method to avoid scratching or damaging the bolt holes. And, additionally ensure that no fluff from the rag is left behind.
The last step is to run a thread chaser through each bolt hold by hand to remove leftover debris. Then you can give each hole a final blast with compressed air.
Please Note: If the thread chaser is difficult to turn (by hand), then the bolt hole is not clean. Conversely, if the thread chaser easily turns, then the bolt hole is sufficiently clean.

Clean the Cylinder Bores
The goal with cleaning the cylinder walls is to use non abrasive equipment. And, if you’re using compressed air, then ensure the dirt blows up, and out, of the cylinders.
Finally, using a clean rag, apply a dab of engine oil, then wipe out each of the bores. Additionally wipe down the exposed parts of each piston.
Please Note: If you’re new to the game of mechanics, then avoid using power tools. As it’s easy to cause unnecessary damage in the process.
Clean the engine block Deck And Cylinder head surface areas
A simple razor blade and a little heat will works perfect in removing leftover gasket material. But if that’s not an option, then using a little brake cleaner and a plastic scraper will do just just fine.
Once everything is clean, use a clean dry rag to wipe down both surface areas. Then finally apply a dab of acetone, and wipe down once more for the final time.
Please Note: Surface areas must be left ‘oil free’, unless otherwise instructed by the vehicles manufacturer

Inspecting the engine
What should you be looking for while inspecting the engine?
The general consensus for inspecting a disassembled engine includes, looking for:
- Signs of physical damage
- Unusual engine wear
- Oil or water contamination
- Visible leaks
- Damaged or worn electrical connections
- and improper prior repairs.
It’s unlikely that you’ll return to this area in the near future. So its important to take full advantage of having the opportunity to inspect the engine at such detail.
The following sections will dive into specific inspections for individual areas of the engine. With each test containing a detailed set of instructions for each step that must be carried out.
Inspecting The Cylinder Head For Warpage
The cylinder head should always be the first point of call (when inspecting an engine for warpage). Being made from aluminium, cylinder heads are more prone to warpage, in comparison to their counterpart, cast iron engine block.
Aside from this, if an engine block were to distort to the point of warping, it would likely include additional symptoms such as, signs of:
- Visible cracks or leaks
- Burning oil
- Damaged cylinder walls
- Engine blow-by
- Or in worst case scenarios, complete failure.
Additionally, because engine blocks are generally cast iron, they retain a higher tolerance to heat, making them less prone to warping when exposed to high temperatures.
That being said, if the car was manufactured in the last ten years, then there’s a high chance that both the cylinder head, and the engine block, are made from aluminium.
Resulting in the entire engine having a lower tolerance to heat than its predecessor.
However, in the event that you discover an engine is warped. Then there is still the option to resurface (i.e. skim) the engine, provided the warpage has not exceeded the manufacturers maximum tolerances.
A great place to find this information is in a Haynes service repair manual, where you find the specific tolerances for the particular vehicle you’re working on.
Inspecting The Engine Block For Warpage
The key difference in testing the engine block vs testing the cylinder head, is down to the fact that the engine block contains cylindrical bores.
As the bores is where combustion takes place. Temperatures can reach as high as 2,500°F (1,370°C) making the area more prone to warpage, than, anywhere else on the engine.
Additionally, as the majority of head gasket replacements are carried out with the engine still in the engine bay. It’s very important to choose a straight edge that is both; long enough to measure the engine, and short enough, to fit in the engine bay.
How to Accurately Carry Out An ‘Engine Warpage test’
Required Tools:
- Feeler Gauge
- Mechanics machined straight edge
- Notepad (or notes app on mobile)
Please Note: Testing must be through and exact. Simply put. At this stage, there is no room for error.
Familiarise yourself with using the tools by placing the straight edge on the flat engine surface, and testing varying sizes of the feeler gauge in the gap.
The image below provides a visual example of how to use a straight edge and feeler gauge for testing.

Checks must be carried out and recorded by following a specific ‘engine warpage check pattern’.
Select the feeler gauge size that corresponds with the manufacturers maximum tolerance for engine warpage. Then begin testing by following the check pattern set below.
The following pattern consists of vertical, horizontal and diagonal checks that should be made when testing for warpage on a 4 cylinder engine.
However, if you are testing an engine that has five or more cylinders. Then the same check pattern should be replicated for the number additional cylinders that the engine contains.

How To assess The test results
The following sections below will help you to determine the actions to take based on your test results.
What Is A Fail?
A failure is when the feeler gauge passes under the machined straight edge. The result is that the engine has warped by at least the size of the selected feeler gauge.
What Is A Pass?
On the other hand, if the feeler gauge cannot pass under the straight edge, then the test is a pass. And the result is that the engine has NOT warped to the extent of the size selected on the feeler gauge.
Actions To Take – Based On Test Results.
Depending on your results, will determine what actions to take.
Test Result | Action(s) To Take |
Engine is not warped in any way | Do nothing |
Engine is warped, but has not exceeded the maximum tolerance | Take engine to a professional machine shop for resurfacing |
Engine is warped to an extent that is beyond the maximum tolerance | Replace entire engine (or at least the part of engine which has warped) |
typical Maximum ‘warpage Tolerances’
The next section will provide examples of tolerances in engine warpage you can typically expect to find for a few of the most current popular selling cars.
Disclaimer: The values in the following tables are “general guidelines”. Engine specifications and tolerances can vary significantly across manufacturers. Always refer to the vehicles service manual for the most accurate information.
Below are the typical tolerances for varying engine types categorised by number of cylinders.
Engine Configuration | Material | Max Warpage (inches / mm) | Action |
---|---|---|---|
Inline 3 (I3) | Aluminum | 0.003 in / 0.076 mm | Resurface/Replace |
Flat 4 (Boxer 4) | Aluminum | 0.003 in / 0.076 mm | Resurface/Replace |
Inline 4 (I4) | Aluminum | 0.003 in / 0.076 mm | Resurface/Replace |
Inline 6 (I6) | Aluminum | 0.004 in / 0.102 mm | Resurface/Replace |
Flat 6 (Boxer 6) | Aluminum | 0.004 in / 0.102 mm | Resurface/Replace |
V6 | Aluminum | 0.004 in / 0.102 mm | Resurface/Replace |
V8 | Aluminum | 0.004 in / 0.102 mm | Resurface/Replace |
V10 | Aluminum | 0.005 in / 0.127 mm | Resurface/Replace |
V12 | Aluminum | 0.005 in / 0.127 mm | Resurface/Replace |
Here’s a chart summarising the cylinder head warpage tolerances for 10 popular vehicle makes and models in the UK:
Manufacturer | Model (Engine Model) | Material | Max Warpage (inches / mm) | Action |
---|---|---|---|---|
Ford | Puma (1.0L EcoBoost I3) | Aluminum | 0.004 in / 0.102 mm | Resurface/Replace |
Kia | Sportage (1.6L T-GDi I4) | Aluminum | 0.003 in / 0.076 mm | Resurface/Replace |
Nissan | Qashqai (1.3L DIG-T I4) | Aluminum | 0.004 in / 0.102 mm | Resurface/Replace |
Volkswagen | Golf (1.5L TSI I4) | Aluminum | 0.004 in / 0.102 mm | Resurface/Replace |
Vauxhall | Corsa (1.2L Turbo I3) | Aluminum | 0.003 in / 0.076 mm | Resurface/Replace |
Hyundai | Tucson (1.6L T-GDi I4) | Aluminum | 0.003 in / 0.076 mm | Resurface/Replace |
BMW | 1 Series (1.5L Turbo I3) | Aluminum | 0.003 in / 0.076 mm | Resurface/Replace |
MG | HS (1.5L Turbo I4) | Aluminum | 0.003 in / 0.076 mm | Resurface/Replace |
Audi | A3 (1.5L TFSI I4) | Aluminum | 0.004 in / 0.102 mm | Resurface/Replace |
Volkswagen | T-Roc (1.5L TSI I4) | Aluminum | 0.004 in / 0.102 mm | Resurface/Replace |
Heres a list with the top selling US vehicles in 2023 and their associated warpage tolerances:
Manufacturer | Model (Engine Model) | Material | Max Warpage (inches/mm) | Action |
---|---|---|---|---|
Ford | F-150 (3.5L EcoBoost V6) | Aluminum | 0.003 in / 0.076 mm | Resurface/Replace |
Chevrolet | Silverado 1500 (5.3L V8) | Aluminum | 0.004 in / 0.102 mm | Resurface/Replace |
Ram | 1500 (5.7L HEMI V8) | Aluminum | 0.004 in / 0.102 mm | Resurface/Replace |
Toyota | RAV4 (2.5L I4) | Aluminum | 0.002 in / 0.051 mm | Resurface/Replace |
Honda | CR-V (1.5L Turbo I4) | Aluminum | 0.003 in / 0.076 mm | Resurface/Replace |
Nissan | Rogue (2.5L I4) | Aluminum | 0.002 in / 0.051 mm | Resurface/Replace |
Jeep | Grand Cherokee (3.6L V6) | Aluminum | 0.003 in / 0.076 mm | Resurface/Replace |
GMC | Sierra 1500 (5.3L V8) | Aluminum | 0.004 in / 0.102 mm | Resurface/Replace |
Toyota | Corolla (1.8L I4) | Aluminum | 0.0028 in / 0.071 mm | Resurface/Replace |
Toyota | Camry (2.5L I4) | Aluminum | 0.003 in / 0.076 mm | Resurface/Replace |
What Is resurfacing (i.e., skimming An engine)?
Engine resurfacing, commonly known as “skimming the engine,” is a machining process where a thin layer of material is removed from the surface area of the cylinder head, engine block, or both.

The purpose of this procedure is to restore a perfectly flat surface, and provide a proper seal between the head and the block with a head gasket installed.
Proper sealing is crucial for maintaining engine compression, preventing coolant or oil leaks, and ensuring overall engine performance.
How much Can Be removed When Resurfacing?
The amount of material that can be removed when resurfacing is directly determined by the distance that the piston must travel, to reach top dead centre (i.e., TDC).
Additionally, this process must ensure that the amount of removed material does not compromise the clearance between the piston head and valves. As reducing the clearance could result in the piston and valves crashing with one another.
The examples below contain the maximum resurfacing tolerances you can typically find for the most popular selling engines.
Make & Model | Engine | Max Skim (Cylinder Head) | Max Skim (Engine Block) | Side Notes |
---|---|---|---|---|
Ford Puma | 1.0L EcoBoost | 0.2mm / 0.0079 inches | 0.1mm / 0.0039 inches | EcoBoost engines are highly sensitive to compression changes, so skimming should be minimised. |
Kia Sportage | 1.6L T-GDi | 0.3mm / 0.0118 inches | 0.15mm / 0.0059 inches | Higher tolerance due to turbocharging. Check the gasket type before skimming. |
Nissan Qashqai | 1.3L DIG-T | 0.2mm / 0.0079 inches | 0.1mm / 0.0039 inches | Small allowances due to the compact engine design. |
Volkswagen Golf | 1.5L TSI EVO | 0.2mm / 0.0079 inches | 0.1mm / 0.0039 inches | Ensure even skimming to maintain combustion chamber shape. |
Nissan Juke | 1.0L DIG-T | 0.25mm / 0.0098 inches | 0.15mm / 0.0059 inches | Similar to Qashqai, care must be taken with turbo models. |
Audi A3 | 2.0L TFSI | 0.25mm / 0.0098 inches | 0.12mm / 0.0047 inches | Performance-oriented, so tolerances are tighter. |
MG HS | 1.5L Turbo | 0.3mm / 0.0118 inches | 0.15mm / 0.0059 inches | Relatively high tolerance for a small displacement turbo engine. |
Hyundai Tucson | 1.6L T-GDi | 0.3mm / 0.0118 inches | 0.15mm / 0.0059 inches | Similar to Kia Sportage, these engines can tolerate more skimming. |
Peugeot 208 | 1.2L PureTech | 0.2mm / 0.0079 inches | 0.1mm / 0.0039 inches | Engine’s compact design requires careful skimming. |
Vauxhall Corsa | 1.2L Turbo | 0.2mm / 0.0079 inches | 0.1mm / 0.0039 inches | Limited skimming allowances due to small engine size. |
Inspecting The Remaining Engine components
The following checklist contains inspections that should be carried out, after the checks on the cylinder head and engine block have been completed.
Carefully follow each of the instructions and take notes where necessary.
Inspect the gasket for signs of wear, cracks, breakage, oil buildup, dark spots, rust, and any deformation or warping that could affect its seal. Note abnormalities, then continue inspecting the remaining components. Check out our examples to visually see how a failed head gasket looks.
Place the cylinder head on a flat surface. Pour a small amount of liquid (like kerosene or fuel) into the intake or exhaust ports. Check if any liquid seeps through the valve seats; if it does, the valves are leaking and need further inspection or replacement.
Inspect the pistons head carbon buildup, cracks, or pitting. On the top of each piston is a spray pattern left from the burnt fuel of the fuel injectors, which is great for comparing inconsistencies across pistons.
Check the camshaft lobes for signs of wear, scoring, or pitting. Rotate the camshaft and visually inspect each lobe for damage. Lobes should be smooth with no rough spots, no indentations or excessive wear.
Inspect the camshaft journals for scoring or wear marks. Use a micrometer to measure the journal diameter, comparing it to the manufacturer’s specifications. Check bearings for wear, cracks, or scoring.
Check each rocker arm for signs of wear, damage, or excessive play. Roll them on a flat surface to identify stiffness. Inspect the rocker arm shafts and bushings for wear or pitting. Replace any damaged components.
Visually inspect the valve springs for cracks or signs of wear, and replace any weak or damaged springs.
Insert the valve stem into its seat (i.e., the valve guide), and feel for excessive play. Too much movement indicates wear in the guide, requiring replacement or reaming with oversized valves.
Inspect the part of the cylinder bore that you can see for any signs of excessive wear, damage or cross contamination.
Inspect all oil passages for blockages or debris. Use compressed air to blow out any obstructions and ensure free-flowing passages.
Inspect the timing chain or belt for wear, cracks, or stretching. Check the tensioner for smooth operation and proper tension. Replace the chain/belt and tensioner if any issues are found.
Check all gasket surfaces for scratches, nicks, or warping. Use a straightedge to ensure surfaces are flat. But ensure to clean first.
Inspect freeze plugs for damage, rust, leaks and corrosion: Freeze plugs, also known as core plugs, expansion plugs, or frost plugs, are small, circular metal plugs in the engine block. They are highly prone to corrosion and usually located down the sides and rear of the engine block.
With the cylinder head and engine block now resurfaced, or within spec. And the remaining components all checked, repaired and replaced.
Its now time to begin reassembling engine.

assembling the Engine
Reaching this point is a great milestone, but still way too soon to take your foot of the gas.
Assembling the engine is essentially doing what you did on removal, in reverse. A simple way to keep track is to use a checklist.
Lets begin with the gasket.
Installing A New Head Gasket
Please note: Some head gasket installations require the addition of liquid seal, while others don’t. So it’s important to check the vehicles service manual for the most accurate information.
Which Side Of the gasket Should Face Up?
Some products have clear instructions, while other don’t. And, unfortunately, in the motor industry; this has seemed to become the norm.
That being said, if the gasket you’re installing has no instructions, then you can also look out for:
- A Branded Label or symbol: Even a manufacturers label on the product will be on the side that must face up
- Colour coding: blue side facing up and black side facing down
- A difference of Texture or pattern: Striped side up and plain or flat side must face down
And if all the above fails, then there’s one last indicator that you might come across.
The answer…. FIRE RINGS!
Not as easy to identify for the newbie DIY engineer, but the difference in design of the fire rings can be a clear indication of the correct way to install the gasket.
The images below provide two examples identifying the differences in design of the fire rings on each face.

Fire rings join with one another. This side must face down and mate the deck of the engine block.

Fire rings are separated. This side must face up and mate the surface of the cylinder head.
If All Else Fails!
Then, there is one last way. But to tell you, I would have to…
Jokes aside, in the case the head gasket has;
- No instructions
- No label or distinct colouring
- No branding
- No differences in texture
- And no differences in design on the fire rings
Then there is one final way, and that way is; there is no other way.
Let me explain.
Most engine blocks contain dowel pins which are uniquely positioned to prevent incorrect instalment of the cylinder head, and head gasket.
In fact, in many cars like my own, the gasket is designed in such a way that it can only fit on the engine block on one specific side, and in one specific orientation. As installing the gasket any other way would result in misalignment of the holes of the gasket, and the passageways in the engine block.
This explains why some gaskets come with no instructions. As being truthful, in some cases; they’re simply not needed.
A few general guidelines to follow when fitting a new head gasket is to:
- Ensure the surface area of the engine block is clean
- Locate the dowel pins on the engine block and cross reference each position with the holes of the gasket
- Test fit the head gasket to ensure all the holes correctly align with the corresponding passages in the engine block (check to that the gasket is also on the correct facing side)
- Fit the head gasket for the final time (in accordance with the manufacturers guidelines)
Installing The Cylinder Head
With the gasket installed, it’s now time to install the cylinder head.
Tools you’ll need:
- Rubber gloves (to lift the cylinder head)
- Assembly lube
- Engine oil
- Torque wrench (for head bolts and bolts in the camshaft journal caps)
- Additionally Use a torque angle Gauge to improve accuracy when tightening bolts
- Liquid marker pen (mechanics pen to mark head bolts)
Install the cylinder head by carrying out the the following steps:
- Put on a pair of protective gloves. As most cylinder heads contain many sharp edges
- Check the location of the dowel pins on the engine block, then Lift the head cylinder onto the head gasket
- Lightly dab some oil onto each cylinder head bolt. This is to reduce the chance of false torque readings as a result of dry threads
- Drop the cylinder head bolts into each of the head bolt holes, then hand tighten each of them. There is no specific order to follow at this time
- Check the service manual for the correct tightening sequence to follow
- Use a torque wrench (and the shortest viable extension bar) to tighten each bolt to the correct torque, while following the recommended sequence (usually starting in the centre and moving outwards) set by the manufacturer.
- Use the liquid pen to mark from 12 o’clock to 6 o’clock Then use this as a reference of where to make turns of particular degrees. Or you can use a torque angle gauge for the most accurate results.
- Install the hydraulic valve lifters (or pushrods) depending on the engine type
- Install the rocker arms making sure to place them back in the correct way, and in the exact locations they came from
- Install the intake and exhaust camshafts to their respective positions and tighten each of the journal caps in the exact sequence set in the vehicles service manual
- Additionally install the camshaft gears if necessary
- Apply assembly lube in all areas where metal on metal contact is present. This includes the top of valve springs, camshafts, pushrods (if you have them), and hydraulic lifters.
- Pour fresh engine oil over the cylinder heads of the entire internal assembly. This will ensure that all components are well lubricated on the initial startup.

Please Note: If the car you’re repairing is chain driven, then you’ll need to install the timing chain and timing cover before you can install the valve cover.
However, if the engine features a timing belt (instead of a timing chain), then you’ll need to install the valve cover, timing cover (if there is one), pulleys, gears, and oil pan, in prior to installing the belt.
Installing A New Timing Chain Or Belt Kit
If you’ve been following this far, and also planned to reuse the existing timing chain (or belt). Then you should have marked and fastened the chain (or belt) as instructed when disassembling.
However, if the car has covered more than 30k miles since the last timing chain (or belt) replacement. Then now is the perfect time to do so.
Tools you’ll need
- A Torque wrench
- A set of Socket and wrenches
- Flathead screwdriver
- Liquid pen (mechanics pen)
- Engine assembly lube
- Engine-specific: Camshaft locking tool
The following section contains a list of general guidelines that should be followed when installing a new timing chain on a majority of vehicles.
- Set the piston of cylinder number one to top dead centre. This can be done by inserting a long screwdriver to the injector hole of cylinder number one. Then to find TDC, rotate the crankshaft pulley clockwise until the screwdriver reaches its highest possible point, before coming back down.
- Align the camshaft timing marks with one another (including the marks on the engine block if required)
- Lay the timing chain or belt over the camshafts and crankshaft gear. Ensuring that the coloured links or timing marks on the belt line up with the associated marks on the gears
- Install the timing chain/belt tensioner (or reset the old one if you’re reusing it)
- Re check all timing marks are aligned to their correct positions
- ‘Manually’ turn the engine for two full revolutions, then check the timing marks on the camshaft’s line backup as theyYou did at the start. If the timing marks do not realign, then remove the chain or belt, and restart from step number 3.
- Rotate the engine at least 6 more times to ensure the timing is correct.
- Re install the timing cover and continue the reassembly
Re install the remaining components
While the finish line is near, we are not quite there, just yet. Instead, what’s most important at this stage, is to remain focused. As it’s far easier to make mistakes when you think you’re in the clear.
The long and short is. Don’t get complacent.
First things first. Install the valve cover, and tighten each bolt to the recommended torque. Next, install the turbo, install the coolant pipes, install the oil feed pipes, and install the intake and exhaust manifolds.
Next, install the fuel lines, injectors, downpipe and wiring loom. Then, install the air intake system, alternator (if required), and any remaining components that were removed but has not been mentioned.
But do not install the spark plugs (or glow plugs) as we will need these out to run a compression test before starting the engine.
Lastly, reconnect the battery it was disconnected.
Testing and Final Checks
Once the components are back in position, its time to focus on fluids.
Refill All fluids
Top up the coolant in the coolant reservoir, and refill the engine oil to the required level specified on the oil level dipstick gauge.
Prime the oil system
- Ensure the spark (or glow plugs) are removed from the engine.
- Turn on the ignition without starting the car. Leave on for around 6 seconds, then switch off ignition.
- Locate and remove the fuse for the fuel pump (safest option). Or if you cant find it then disconnect the wiring to the fuel injectors (not as safe as may cause flooding of cylinders)
- Crank the engine for 10 – 15 seconds making sure to rest the engine for at least 2 minutes between cranking.
- Repeat the previous step (i.e., cranking) 3 more times, then re attach all components (except the wiring to the fuel injectors if already disconnected).

Bleed the Fuel System (diesel Cars Only)
As most petrol engines are self priming, you will only be required to complete this step on a diesel.
The short explanation is: If working on a diesel engine then always bleed the fuel system.
Please note: You should NEVER skip this step on a diesel engine as doing so will 100% catch you out if the engine does not start after the rebuild. Don’t skip it.
The long explanation is: Modern diesels that feature a common rail system will typically inject fuel at 15,000 to 30,000 psi (around 1,000 to 2,000 bar), while a petrol fuel system will inject at just 500 to 3,000 psi (about 35 to 200 bar).
With diesel fuel having a higher flash point (typically 52-96°C (126-205°F) over petrol at just -43°C (-45°F), diesel is inherently more difficult to ignite, and in turn, more susceptible to air contamination.
The higher flash point of diesel means it is unable to vaporise as readily as petrol. Resulting in the need for diesel to be injected at higher pressure in order to create the mist (of atomised fuel) that is required for effective combustion.
This procedure will require a second person, so grab a friend for some assistance:
how to Bleed a diesel engines fuel system
Note that some diesel engines will have a bleed nipple, but Iv’e found this method to be often ineffective
- Slightly slacken the nut (just one) of the first high pressure fuel line that mounts to the fuel injector (as highlighted in the image above)
- Crank the engine for 10 – 15 seconds until you see bubbles. Then continue cranking until you see a steady stream of diesel running with no bubbles
- Tighten the nut once you are confident there are no more bubbles (i.e. contaminating air) in the system
- Repeat the previous steps for the remaining fuel injectors (i.e. cylinders) on the engine
Once this is done, move onto the test below.
Perform an engine compression test
Please note: You will need a second person to perform this test
Note the satisfactory minimum and standard compression readings shown in the vehicles service manual. Additionally note the maximum allowable pressure difference between cylinders in the service manual.
- Remove all spark plugs (or glow plugs) from the engine.
- Unclip wiring to the fuel injectors (or remove fuel pump fuse)
- Insert (screw in) the long tube of the compression tester to the spark plug (or glow plug hole) of cylinder one
- Crank the engine for 10 – 15 seconds
- Note the reading and leave for 2 minutes and recheck reading to ensure that pressure additionally held at initial level
- Release the pressure in the compression tester (via the pressure release valve)
- Rest engine for around 2 minutes
- Repeat this process for remaining cylinders on the engine (making sure to take detailed notes)
Assessing the results.
- If the readings of any cylinders were lower than the satisfactory minimum compression level specified in the vehicles service manual, then there is a fault in the specific cylinder that must be further investigated
- If the readings across each cylinder is by a larger margin that what is allowable by the manufacturer, then there is a fault in one or more cylinders that must be further investigated
- If compression readings are within the satisfactory limits set by the manufacturer, then the test is a pass and the repair is complete.
- If the difference of readings across cylinders does not exceed the maximum allowable tolerance set by the manufacturer, then the test is a pass and the repair is complete.
Visually Inspect The Engine
The purpose of a visual inspection is to identify abnormalities before starting the engine. This could be a leak, crack, loose nut or bolt, damaged wire or missing part.
Inspect, inspect, inspect. You can never check too much, as now is the time where you want to fix problems as opposed to when the engine is running and under stress.
Once you are happy with the checks, it’s time to move onto the final stage.
Fire Up The Engine
Reconnect the remaining components which have been removed. I.e., glow plugs (or spark plugs), and fuel injectors.
Remember: The engine requires three elements to successfully start and run
- Air
- Fuel
- Ignition
Ensure that all fuel lines are good and injectors are good. Ensure air filter, intake manifold and turbo (if you have one) is good.
Then ensure connectors and bolts for fuel injectors are good.
Next, crank the engine for 10 – 15 seconds.
Continue checking while cranking for
- Unusual sounds
- Leaks
- Unusual Smells
- Excessive smoke in a particular area – although a little smoke is 100% expected on first start up
If the car starts, then woohooooo! Well done. But we are not finished yet.
On the other hand, if the engine doesn’t start, then do not worry. However, you will need to go back and investigate the following areas:
- Air system
- Fuel system
- Ignition system
Stationary Vehicle Assessment: How Does The Engine Run?
With the engine running, it’s now time to assess the following:
- Does the engine misfire run smoothly?
- Is there excessive smoke coming from any area of the car?
- Is the coolant bubbling in the reservoir?
- Does the in car heating work?
- Are all lights working?
- Are the fans kicking in at the correct time to cool down the engine?
If any of the above is a fail, then switch off the engine and investigate.
If everything is good, then it’s time to take the car for a test drive.
Driving The Car For the first Time
The first drive of the car should be focused on assessing the engine’s performance, unusual lights on the dashboard and unusual smells.
Drive the car for around 15 minutes making sure to use a variety of roads that include hill climbs, downhill gradients and a series of turns.
While driving you should make the following checks:
- Is the temperature gauge building up or remaining at normal?
- Can you hear unusual sounds such as engine knocking, grinding or whining?
- Is there excessive exhaust smoke?
- Are there any warning lights on the dashboard?
- Are there unusual smells coming inside the cabin?
Once you return back. Re perform the stationary vehicle assessment.
5 Mistakes To Avoid When replacing A head gasket
I’ve seen and made a whole bunch of mistakes in the past. But the following five in this list are among the most common, and most costly, I have personally witnessed.
Innocently trying to save time, or save money can become real expensive. So here’s a few ways to avoid it.
Mistake #1 – The Worst And most common
Reusing old cylinder Head stretch bolts
I’ve come across YouTube videos with others making this mistake. Let me be clear. AVOID doing this, at all costs.
Cylinder head bolts are designed to stretch. Meaning, when you tighten them down, they elongate. Resulting in them having a one-time-usage.
For one, there is already a confirmed failure in this area. So why take the risk of having to make this entire repair again?
By far this is the most common mistake, and can result in a cracked engine block, continued failure or non starting engine. Avoid.
Mistake #2
improper Engine cleaning (When Disassembling)
The short and sweet is, don’t rush this repair.
Failing to thoroughly clean the engine block deck and cylinder head surface areas is a fast track to failure.
Both surfaces must mate with a flush fit to create an effective seal. Dirt or debris in this area can result in improper sealing, and low engine compression.
Furthermore, tightening down an offensive object between two flat surfaces can result in cracks, leaks and false readings on torque wrenches.
So always ensure to thoroughly clean surfaces and bolt holes as objects or particles in these areas are notorious for resulting in unnecessary issues.
Mistake #3
Not taking the cylinder head to a machine shop
This mistake is an odd one. It never really matters till the engine is pieced back together, and a new problem presents itself.
That’s when it becomes vital. As you begin to question if there was a crack, leak or uneven surface that you missed hen making the repair.
And for what is usually a cost of less than £100, it is well worth taking the engine to a professional machine shop. This way you can be confident that you are rebuilding an engine with no further faults.
A DIY toolkit has its limitations. Point blank period. So let the professionals do what they do best.
I have personally made this mistake in the past. Only to find out that I had to start out all over again after already rebuilding the engine.
AVOID!
Mistake #4
Misdiagnosing the issue (i.e., Making Assumptions)
Ever realised that everyone becomes an expert whenever your car develops an issue. I have.
But simply following the information of others without a clear diagnosis can lead you straight down a path to disappointment.
Instead, always carry out a proper fault diagnosis and correctly identify the faults before starting the repair.
Mistake #5
Using poor quality (or incorrectly installing) parts
Ever heard the saying “You get what you pay for”.
There’s some truth to this.
As cheaping out on parts is a fastrack to failure. Vital engine components should not be messed with.
And besides, if you’re already saving on labour cost, then why not go all in on quality.
The second part of this mistake is made by not following manufacturers guidelines in installation. Long story short, if it’s not in the book, then don’t do it.
This means, no liquid gasket, no washers and no missing or skipping torque settings. AVOID!
I have made this mistake many times and paid the cost. Don’t do it!
Questions To Ask (Before Carrying Out This Repair)
A head gasket can fail for a number of reasons, but the most common is because of overeating. So the question to ask is, what causes an engine to overheat.
In which the reply is; from a faulty water pump, thermostat, radiator, fan, low coolant levels, or lack of lubrication.
Surprisingly, aside from a torque wrench, and potentially a straight edge, there are not any special tools required to replace a head gasket. Instead, the success of the replacement directly correlates with the access you have to the manufacturers guidelines.
A professional mechanic with all parts to hand can complete this repair in 5 hours. However, a DIY mechanic with no ramp, previous experience, or access to professional equipment will typically take around 8 hours to 3 days to complete this repair.
The short answer is; it depends. As the only time a sealer would work is if the gasket is partially blown. There are no guarantees.
And besides, I am yet to find a liquid sealer that repairs a physically damaged metal component.
So the only time a sealer would make sense is if you needed to get the car home (to make the repair), or to a scrap yard.
A blown head gasket is not always an indication of a damaged engine. But it certainly is an indication of an engine operating incorrectly.
As a gasket is designed to take the hit when the dominoes begin to fall, it is first inline to blow before anywhere else in the engine is damaged. Because of this, it’s totally possible to find a blown head gasket with all other components intact.
A successful head gasket replacement will result in a smooth delivery of power, consistent idle, and normal operating temperatures. Additionally, there should be no leaks, no fluid contaminations, and no reduction in levels of the engine’s compression.
Failing to promptly replace a blown head gasket will in all cases result in complete engine failure. Oil mixing with coolant, or either fluid escaping from their normal pathways will result in poor lubrication, inadequate cooling, and catastrophic internal engine damage.
The most common type of gasket used in modern cars are MLS (multi-Layer Steel) gaskets usually consisting of 3 – 5 layers. To date, they retain the most durable and cost effective design.
But it’s also common to find copper gaskets Elastomeric (i.e., silicone) gaskets used in performance cars. And while they are more expensive, they offer far better durability, flexibility, and increased tolerance for a wide range of applications.
Replacing an engine’s head gasket will always reduce the car’s resale value for honest sellers. The simple reason is; an engine which has never had issues is far more appealing to a wider range of buyers over an engine that is like frankenstein.
Yes, cross contamination of fluids will always result in an increase of emissions. And the result of increased emissions equals excessive exhaust smoke.
The short answer is never. Or in other words, when it blows. As a head gasket in a well maintained vehicle can last the lifetime of the engine. With the average lifespan for an engine being 150,000 miles, a head gasket should last just as long.

Unexpected problems That Can occur replacing The Head Gasket
Sometimes things just don’t go as planned. And that’s ok!
But that doesn’t mean you should give up. As through trial and error is learning. So stick to it, and you’ll figure it out.
I love to live by “most things are repairable. It’s just that, some things are more expensive to repair than others”.
Regardless, here are some common issues that you may come across after a head gasket replacement;
- Coolant or oil leaks
- Overheating
- White smoke from the exhaust
- Loss of power or misfires
- Coolant contamination in the oil (or vice versa)
- Improperly torqued head bolts
- Air pockets in the cooling system
- Warped or cracked cylinder head or block
- Improper timing
- Excessive oil consumption
- Exhaust gas in the cooling system
- Check engine light
- Water pump or thermostat failure
- Poor fuel economy
Any of the above warrants further investigation. But don’t beat yourself up. As in most cases a simple tweak is all it needs.
Further issues you might see include:
- Engine management light – This can result from disconnecting various mechanical components resulting in the ECU detecting a fault or miss reading when reconnected
- Malfunctioning electronics (inc keys and alarms) – The battery being disconnected for an extended period of time can result in particular components requiring reprogramming to function correctly again. The good news is that if the engine is running then rest is a piece of cake.
How to prolong the life of a head Gasket
The most effective way to extend the life of a head gasket is to prevent driving a car when the engine is overheating. This means, faulty thermostat, stop, faulty fan, stop, faulty whatever it is, stop, call a recovery and prevent the cause of further damage.
Aside from this, making sure that coolant is always topped up, and not leaking. Making sure that oil is topped up, and not leaking are the two best ways to maintain the life of a head gasket.
Conclusion
The most hilarious part of this post is the fact that it took longer to write this post than to make the repair.
And while a head gasket failure is a major issue, I hope that this post was able to simplify the concepts, amplify the symptoms, and help you to define a clear path for the repair.