What Causes A Blown Head Gasket?

By on 28 October 2020 / Leave a comment Updated on: 3rd February 2021

Often a question that goes unanswered. Car troubles, aside from being expensive, are a real annoyance and a big disturbance in our daily schedules. Chances are, most of us likely get the issue fixed as soon as possible, receive the car back and return on our merry way. Then, when problems resurface weeks or months later, we are shocked, appalled and annoyed all over again. Some will be tempted to ignore the problem and keep driving without replacing a failed head gasket, take it from us though, this is a really bad idea.

Addressing the underlying issues can often be a lengthy, time consuming and expensive processes, but a worthwhile one nonetheless. Sort the problem at the source and you’re unlikely to see issues arise again. Not only will this save money and time in the long run, but will make life easier. Having a vehicle, you can rely upon makes a packed schedule easy to maintain and keeps stress low. Understanding first, the reason the head gasket has failed, will undoubtedly help you prevent it happening again.

The 3 Main Reasons that Head Gaskets Fail


Undoubtedly the most common reason for head gasket failure. An engine that is overheating causes expansion of its metal components. Different parts of the engine will expand at different rates, in particular the head and engine block (the components the head gasket is sandwiched between). As the two expand at different rates the head gasket can be crushed or snapped. Metallic parts can be permanently warped by overheating, meaning the gasket will never seal the two again until repairs take place.

Overheating can be caused by a huge variety of issues. Low coolant or blocks in the coolant system are some of the most common and easy to diagnose/ fix. Leaking is easy to spot so check all the pipes and connections around the cooling system. Failures of the more expensive hardware such as the radiator or water pump are also not uncommon, these may be easy to spot a leak from. If no leaks are obvious then there could be internal damage, blockages or faulty sensors and thermostats that will need replacement or a specialist diagnosis.

Lastly, overheating can sometimes be caused by non-mechanical factors. Driving too fast in high temperature conditions or up steep hills increase stress and temperature. Sitting in heavy start-stop traffic can also cause overheating, as no air flows through the radiator. Always keep an eye on your temperature gauge in these conditions to spot any irregularities that will make it easier for you/ a trusted professional to diagnose overheating problems.

Pre-Ignition/ Detonation

Another common, yet relatively unknown, reason for head gaskets to fail. Detonation (sometimes referred to as spark knock) is another culprit of an engine not running at its finest, that could cost you big. The term “detonation” refers to the pre-mature combustion of fuel, which causes huge pressure spikes and hence added force onto the head gasket. Repeated instances of this can easily causes cracks in the gasket, allowing pressure to escape.

Detonation is often caused by fuel of poorer quality than the vehicle may require. This may be purely down to a poor batch of fuel at a less than trustworthy fuel station or may be a result of running a modified/ highly strung performance vehicle on standard “non-premium fuel”. Incorrect ignition timing and faulty EGR systems can also be culprits that lead to spark knock, often difficult to identify unless looked at by a professional or well-versed home mechanic.

The best way to avoid detonation or knock is to always get fuel from trusted sources and ensure you are meeting the octane rating suggested in the owner’s manual, utilising octane boosters if necessary.

Poor Design or Installation

Last, but by no means least, is a poorly designed or installed head gasket. This seems like something trivial, that should not be causing failures on a mass-produced vehicle. It is, however, surprising the amount of fully developed cars that can leave the factory only to start blowing head gaskets due to poor quality parts or design. Often suppliers can provide poor quality parts, conditions may change and driving habits may not reflect the conditions in which the parts were originally tested.

Incorrect fitment by the manufacturer or garage (when performing repairs) is not common but is a simple mistake that many have made. Head gaskets look very similar from both sides and both ways around, meaning a rushed job or slightly confusing instructional manuals could make for seriously embarrassing mistakes. A head gasket not installed properly will likely not seat against the parts correctly (if at all), allowing pressure out and fluids in.

The best way to avoid failure in this case is to make sure you are well versed on your car’s common faults from knowledgeable sources (web forums are usually a good start), making sure any recalls have been performed when buying a used vehicle. In the case of having the gasket replaced, ensure you take your vehicle to a well-trusted professional, who will complete the repairs up to and above the required standards.

Advice to Prevent Head Gasket Failure

The best method of preventing failure is to address any small problems before they can manifest into larger issues. This is particularly important of your cars cooling system. A leaky hose or dripping radiator may seem a small annoyance but can quickly lead to expensive failure. Hence, keeping your vehicle in the best condition possible, getting it serviced correctly and using good quality fuel could mean the difference between thousands of trouble-free miles and thousands of pounds spent at the local garage. That means not turning the music louder when a new noise appears and getting those advisories fixed from the last MOT, even if your car passed without fixing them.

A leak-free cooling system, fuel up to the manufacturers standard and a trusted mechanic or skilled DIYer is all that is really required to prevent head gasket failures.

Some vehicles may, unfortunately, be highly prone to failure, due to poor quality manufacturer parts. In this case being proactive may save you some stress. Replacing the gasket with a higher quality item before it can fail may not save you any money, but can be done when you decide without worry or stress of being without your vehicle.

Keeping an eye out for the symptoms of head gasket failure is also important to spot any issues that are unfortunately rising to the surface. Addressing the failure sooner, rather than later could save you thousands from possible engine damage and rebuilds.


Big bills caused by small annoyances. That leaky pipe that would have cost you ten pounds and ten minutes, could well turn into a head gasket failure that will cost you thousands and leave you stranded. You don’t want to join the hard shoulder crowd, ruining that long-planned family holiday or all-important meeting.

Get the basics right and you’ll be trouble free. Keep an eye out for any symptoms and keep that vehicle in the condition it deserves. After all, if you treat your vehicle well it will treat you well in return.

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Jack Gill

Car journalist and fully qualified mechanical engineer, Czok’s newest contributor and long-time automotive writer. Lifetime passion for all things automotive, from new supercars to rusty old hatchbacks. If I’m not behind the wheel, I’m likely under the bonnet or browsing the classifieds. Having spent over 5 years in the automotive industry and under the bonnet of my own car at home, I want to share the knowledge and learning that I have gained, with others without the time to study or the expertise, who just want their car to get them from A to B every day. We aren’t all interested in trawling through endless internet pages and forums. I aim to gather all the information up and roll it into a quick summarised format, to give only the information you really need.

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