What Causes Head Gasket Failure, And How You Can Prevent It

The head gasket is one of the most important gaskets in a car and if it fails, can spell catastrophe for your beloved motor. To potentially save your car, here are the basics of this potential car killer and how to avoid trouble
What Causes Head Gasket Failure, And How You Can Prevent It

What does a head gasket do?

What Causes Head Gasket Failure, And How You Can Prevent It

As gaskets go, the head gasket is probably the most important within a car. Its job is to seal the combustion chambers and the coolant and oil passages between the engine block and the head. These are very important areas to keep sealed and apart from each other as the combination of unwanted coolant entering a cylinder or the oil supply is a recipe for disaster. A head gasket therefore is generally designed to never fail or need replacing, with the long bolts of the engine block squeezing it in place to a desired tolerance.

What happens when it fails?

What Causes Head Gasket Failure, And How You Can Prevent It

Depending on where the head gasket fails, different levels of damage can occur. If, as I experienced, your head gasket goes at a point that once separated cylinder and coolant, you can end up with a quickly overheating engine followed by steam pouring out of the exhaust and eventually a loud bang as your engine gives up the ghost.

If you’re lucky, only a small failure in the gasket will occur which can be noticed through small decreases in coolant over time and yellow gunk floating around in your oil and caking the oil cap - the result of coolant entering the oil system and mixing. Temperature gauges will also sit slightly higher than standard as liquid is lost from the cooling system.

Although the gasket itself is inexpensive, the labour involved in dismantling the engine to replace it can be vast. To perform the replacement properly, the engine head will need to be extensively checked for any damage and may need to be skimmed to make sure its flatness hasn’t been compromised by overheating. Skimming is the milling of the cylinder head on a milling machine to take a very thin layer of material off the top of the head to ensure complete flatness; any small gaps will only ever lead to future failures.

What causes it to fail?

What Causes Head Gasket Failure, And How You Can Prevent It

One cause of head gasket failure is pre-ignition. As fuel is combusted at unwanted times during an engine’s cycle, large pressures can occur within the cylinder head as the engine begins to work against itself. These spikes in pressure can put strain across the head gasket, causing it to fail.

Overheating is another possible cause, as the gasket is placed under conditions over and above its design criteria, resulting in warping and permanent damage. This can be purely down to coolant leaks from a corroded radiator or dodgy piping, or it could be pre-existing failures in the head gasket.

Known elegantly as 'mayo', this yellow gunk is formed as hot water and oil mix together due to a gasket leak, an instant giveaway for head gasket failure
Known elegantly as 'mayo', this yellow gunk is formed as hot water and oil…

Another sub-section of overheating is the way in which your engine warms up. The gaskets within an engine are specifically designed to contain thermal properties that allow them to expand and contract as the engine warms up and cools down respectively. Hopefully as petrolheads you all know that you should wait for the engine to warm up fully before putting the foot down. I personally keep my engine speed below 3000rpm before my temperature gauge is nice and stable. But over-rev while cold and the engine and head gasket will be put under extreme thermal stresses as it expands too quickly, which can result in gasket failure as well as cracks in the head itself.

Poor gasket design can also be a car killer. A famous case of a head gasket that couldn’t cope with the thermal stresses placed upon it during its associated engine life was within the K-Series. Produced by Rover in the 1980s, the K-Series went on to feature in MGs, Lotuses and Caterhams due to its lightweight construction. The K-Series engine was revolutionary in its design, using a sand cast which had liquid aluminium poured into it. Long bolts were then used to hold together the different parts of the engine and torqued up to sandwich the K-Series together. Unfortunately, the standard gaskets were not suitable for the interaction with the aluminium engine block and thus were prone to failing as early as 40,000 miles into the engine’s life.

The MG ZR and Caterham 7 both used K-Series engines back in the day
The MG ZR and Caterham 7 both used K-Series engines back in the day

Strengthened gaskets can be found on the aftermarket, using different combinations of composites to add to their strength under vast changes in temperature from engine start up to peak operating conditions. Despite the hassle involved with changing the head gasket, the long term advantages of doing so could be enormous, potentially saving your car from the scrapyard.

It can be a complete lottery in terms of where failures on the gasket occur and therefore the range of potential damage is fairly extreme. From simply a small lack of coolant to a potential car killer, ‘HGF’ is not something to be taken lightly. So check your oil, check your coolant and always allow your engine to warm up before a hoon!

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Comments

house

Nice article!

06/12/2016 - 09:10 |
4 | 0
Dzonny the e36 maniaq

“A head gasket therefore is generally designed to never fail or need replacing” sorry but this doesn’t sound true, they fail all the time and it’s normal that they have to be replaced sometimes. But correct me if I’m wrong

06/12/2016 - 09:12 |
2 | 2

Its “designed” to not fail, but with most cases its the costs or poor build quality which limit the reliability of the parts involved.

06/12/2016 - 09:59 |
2 | 0

True! Well, only partially true. You see, they are designed to never fail or need replacing… during the life of the car. And that’s why it looks like that statement is wrong, because the life of the car isn’t the life of the car. The life of the car is 250 000km. That’s the car’s life, as decided by its designers.

When engineers build engines, they build them to last 5000hours on the test bench. Since the average speed of the whole life of a car lies around 50kph, the engine is designed to last 5000*50=250 000km.

So the head gaskets are designed to last 250 000km under normal use of the engine. If the engine is abused then they won’t last as long, and after 250 000km there’s really no guarantee on if it will last or fail.

06/12/2016 - 10:00 |
4 | 0

Everything is designed not to fail. But it does :p

06/12/2016 - 11:43 |
0 | 0
Anonymous
06/12/2016 - 09:20 |
34 | 2
Di Zazzo

In reply to by Anonymous (not verified)

I red that with Borat accent. ..

Lol

06/12/2016 - 23:12 |
6 | 0
Anonymous

Yeah, my car coolant needs to be filled up about every 1-2 months or so. I would assume its a head gasket leak

06/12/2016 - 09:21 |
0 | 0
Bartek Tymoszuk

In reply to by Anonymous (not verified)

It might be as well a very small crack in a radiator or loosened coolant hoses. If you got an engine cover underneath, coolant accumulates on it and you can’t even notice stains on the ground.

06/12/2016 - 09:56 |
8 | 0
Arno

In reply to by Anonymous (not verified)

Are you sure it’s not leaking somewhere else? Like in the interior radiator. Check the whole system first before replacing the head gasket.

06/12/2016 - 10:01 |
2 | 0
Anonymous

In reply to by Anonymous (not verified)

There are tell tail signs. Look at your exhaust as you cold start the car and look for white smoke. That’s a dead giveaway. White milky residue around the oil cap.

Check everywhere for leaks, then check that and Google the symptoms of a head gasket. If there are no coolant leaks you’ll probably want to get it pressure tested.

06/12/2016 - 10:52 |
2 | 0
Anonymous

In reply to by Anonymous (not verified)

I had that. It was a simple rubber that cracked. Thankfully, wasn’t a HGF

12/10/2016 - 13:32 |
0 | 0
Anonymous

Very helpful!

06/12/2016 - 09:51 |
2 | 0
Bartek Tymoszuk

So basically, not driving like a maniac on cold and letting the engine cool down after hooning or long trips are the only things that can prevent it, as it’s mostly a random thing, or a design fault. Like I thought, you never know when it can happen.

06/12/2016 - 09:53 |
0 | 0
Oscar Taylor

We thought we might have a head gasket leak on our 2009 Volvo XC60 due to loss of coolant - turns out it was just a hose leak! Phew!

06/12/2016 - 09:59 |
30 | 0

You got Lucky :)

06/12/2016 - 16:54 |
2 | 0

same here with the golf I used to have!

06/13/2016 - 07:21 |
0 | 0
Anonymous

That is a nice cake mold (Thumbnail)

06/12/2016 - 10:05 |
2 | 0
Vw Gas Auto

When i saw the picture, i thought someone filled the head gasket up with chocolate cream, and tries to bake it in a oven!
HAHAHA WTF

06/12/2016 - 10:18 |
206 | 4

Me too lol

06/12/2016 - 11:41 |
10 | 0

I think someone will have an idea to make a cake or pudding with head gasket😂😂

06/12/2016 - 11:54 |
8 | 2

I thought the same thing. Either that or I’m just hungry af right now lmao

06/12/2016 - 18:37 |
2 | 0

As did i. Actually clicked for tips on baking with car parts. =P

06/12/2016 - 21:46 |
0 | 0

comming up as comment of the week ;)

06/13/2016 - 18:26 |
0 | 0
Anonymous

Biggest head gasket killer is a car overheating and people keep driving it rather than instantly pulling over.

Ask me how I know.

06/12/2016 - 10:43 |
66 | 0
🎺🎺thank mr skeltal

In reply to by Anonymous (not verified)

How do you know?

06/12/2016 - 11:29 |
36 | 0
[ Insert Name Here ]

In reply to by Anonymous (not verified)

R.I.P lmfao

06/12/2016 - 11:42 |
0 | 0
TheStigsAmericanCousin

In reply to by Anonymous (not verified)

just buy an aircooled volkswagen, they don’t have head gaskets at all! so you can overheat all day and simply brake every other part

06/12/2016 - 20:36 |
28 | 0
Anonymous

In reply to by Anonymous (not verified)

Only times ive heard head gasket failure has always been from overheating in heavy traffic or leak in radiator.
I blew head gasket from a V6 Mondeo because it had radiator leak. Couldnt fix the radiator so i decided to see how far it goes.
Around 500km of constant redlining and it died. :D it was going to be scrapped anyways

06/19/2016 - 07:35 |
0 | 0