I’ve used head gasket sealants in the past with reasonable success. Some people swear by them, but I would only use a sealant as a temporary fix until you can get the head gasket repaired properly.
Matt Wrankmore
Head of FixMyCar's Garage Network
Guide to Head Gasket Sealants
FixMyCar discusses when you can use head gasket sealant and how it works.
Book a car repair nowEllie Dyer-Brown
Wednesday August 06 2025
4 min read
The head gasket is a vital component that you probably don't think about until a problem arises. Over time, it can become worn and lose compression, allowing coolant and oil to leak into the cylinders.
Head gasket replacements can be costly, so you might want to try fixing the problem with the help of sealant. But how does it work, and what are the best brands? Find out in this guide.
What is head gasket sealer?
The function of the head gasket is to seal the internal combustion chamber and to allow coolant and oil to move through the engine without mixing. When the seal is too loose or develops cracks, it can have severe consequences for the engine, especially if you continue driving. For this reason, if there is an issue with the head gasket, it should be dealt with promptly to ensure no more problems occur, and sealant can help with this.
Head gasket sealant fills in the cracks on a damaged head gasket. It forms a seal that prevents further leaks from occurring, effectively patching up the damaged area. It is a stop-gap solution but shouldn't be relied on in the long term for major leaks.
Do head gasket sealants really work?
Head gasket sealers are effective at fixing minor leaks and will last around six months for more severe damage. However, the effectiveness of a sealant depends on its quality and how you use it.
The amount of sealant you need will depend on the size of your engine. For example, cars with four or six cylinders generally need less sealant than those with eight or ten cylinders.
What is the best product to seal a head gasket?
There are many different types of head gasket sealers on the market, so it can be hard to know which to choose. Below are the top three products available based on reviews.
BlueDevil Head Gasket Sealer
Steel Seal Head Gasket Repair
K-Seal ST5516 HD
These different sealers are all simple-to-use solutions from well-established brands, and depending on your exact needs, you should find top results from using each of them to seal up your head gasket. Prices vary from store to store, so shop around for the best price.
How long does head gasket sealer last?
How long your head gasket sealer lasts will depend on the extent of the damage. Different brands have different ingredients; some will last longer than others. While head gasket sealant can offer a permanent fix to minor leaks, more severely damaged head gaskets will last for only up to six months.
Check out our complete head gasket repair guide.
Where do you put head gasket sealant?
Head gasket sealant should be introduced to the coolant system through the radiator cap or the expansion bottle, depending on your car. Always make sure the engine is cool before you start.
Will head gasket sealer stop an oil leak?
Sealant will fix an oil leak as long as the leak is due to a faulty head gasket. Here are some other reasons why your car might be leaking.
Is head gasket sealer worth it?
Head gasket sealer may be worth purchasing, depending on the extent of the damage to your head gasket. Minor leaks can be sealed permanently, but sealant only stops more significant leaks for around six months - in this situation, a head gasket replacement is inevitable.
Will head gasket sealer ruin an engine?
As long as you use the correct sealant and apply it by following the instructions, it won’t cause any damage to your engine. In some situations, using head gasket sealant is a safe way to re-seal your head gasket without having to pay for a costly replacement.
Head gasket sealant is often only a temporary solution, especially if the damage to the part is severe. An alternative option is to book a head gasket replacement, which costs £720.10 on average, according to FixMyCar's data.
If you found this guide helpful, you might also like:
Get quotes in minutes
Save money on your car repair
Ellie is FixMyCar's Content Manager. She has over three years of experience writing about cars and regularly collaborates with automotive experts to provide trustworthy advice for drivers that is easy understand. Her work has been featured in Yahoo! Finance, iNews, The Daily Express and The Sun. She has a BA in English literature and an MA in creative writing from Durham University. Outside of work, Ellie follows F1 and eagerly awaits Ferrari's next era of dominance in the sport. She drives a Suzuki Swift.