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The Best Head Gasket Sealer 2021

fix a blown head gasket

A blown head gasket can cause engine misfires, oil leaks and coolant to mix with the engine oil. To fix a blown head gasket, you have the choice of changing the head gasket completely or using a head gasket sealer.

The best head gasket sealer is the Blue Devil Permanent Repair, which fixes blown head gaskets, warped or cracked heads and a range of other defects.

Head Gaskets are a ringed panel that sits between the engine block and cylinder head, which prevents engines fluids going into the cylinders. As soon as it fails, it can cause a range of issues with your car that can become costly.

Table of Contents

Best Sealer For Blown Head Gasket

Head Gasket SealerPermanentEngine Sizes
Bar's Leak HG-1YesAll
Steel SealYesSpecific
K-Seal ST5516 HDYesSpecific
ATP AT-205NoAll

Simply ignoring the issue and hoping it goes away does work but not with a blown head gasket. If ignored, damage can be caused to the engine and catalytic converter as well as a range of other defects from mixing of fluids.

Purchasing the head gasket is not the expensive part but the man hours replacing it is where it starts getting costly. However, a sealer is an alternative fix that is simply poured into the radiator cap, which then seals any leaks present.

Overtime, the gasket will become weaker and more prone to expensive issues but a sealer can prevent any major bills. Below is a list of the best head gasket sealers that will seal any leaks that are present due to a blown head gasket.

BlueDevil Head Gasket Sealer

Blue Devil is not a well known brand to many mechanics but for those who work with blow head gaskets, it will certainly be known. Blue Devil claim that their head gasket sealer is a permanent repair and guarantees this too.

The formula contains no solids or particulate matter and is safe for all engines. It will repair blown head gaskets, warped or cracked heads, leaking heater cores and leaking freeze plugs. It will certainly prevent very expensive repair bills for many car owners.

It can be used for both gasoline and diesel engines and using the product is fairly straight forward. Simply flush out the old coolant and replace with high quality coolant and then let the engine run for 15 minutes.

After this period, remove the thermostat and add the sealant. The purpose of removing the thermostat is to avoid the computer diverting the sealant aware from certain areas of the engine.

The Blue Devil formula is the best head gasket sealer you can buy and although slightly expensive, is it worth paying the extra. The manufacturer guarantees the repair for peace of mind and its worth using it before replacing the head gasket.

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Bar’s Leak HG-1 Blown Head Gasket Repair

The Bar’s Leak formula is very much similar to the Blue Devil above with the brand stated a guarantee repair for head gasket coolant problems. It even comes with a limited lifetime warranty and reinforced with carbon fiber for good measure.

Carbon Fiber within the formula is very unique and acts as a rebar in concrete to prevent large leaks and produce a permanent seal. It has been purely designed to stop cooling system leaks and it does this very well.

In terms of the application, you should only use this formula with a cold engine and pour it into the radiator and reservoir to the correct level as per the dosage chart. You should then let the car reach optimum temperature and recheck the coolant levels.

Overall, it is the best head gasket sealer for the money with a very reasonable price compared with the Blue Devil alternative.

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Steel Seal Blown Head Gasket Fix

The Steel Seal is a permanent head gasket sealer, which is a go-to product for many professional mechanics as a quick fix. There are many version of this award winning formula with sealers designed for 4, 6 and 8 cylinder engines.

Steel Seal claim that it will permanently seal blown head gaskets, warped heads, cracked blocks and other defects within minutes. They offer a “fixed or refunded” policy and claim a 99% success rate with their lifetime guarantee.

It is by far one of the best head gasket sealers but the price is its major downfall. Considering it is more than three times some of the other premium brands, it can be a gamble but the statistics are certainly something to think about.

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K-Seal ST5516 HD

The K-Seal ST5516 HD is a permanent coolant leak repair that mixes with all antifreeze without the need of draining or flushing. It will fixes blow head gaskets, warped cylinder heads and a range of other engine defects causing leaks.

It is designed for larger capacity engines as well as trucks, tractors and industrial automobiles. It is a heavy duty head gasket sealer and from just one bottle, it will treat coolant system up to 62 liters.

Overall, if you have a large truck with a head gasket or coolant leak, this is the head gasket sealer for you. Blown head gaskets can cost a fortune to replace for large capacity engines such as trucks but this is a cheap head gasket sealer that is highly rated by many truck owners.

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ATP AT-205 Re-Seal

APT AT-205 is not marketed as a head gasket sealer as such but it is a product that is highly effective at stopping leaks with engines, power steering and differentials.

The formula includes AT-205, which is a known plasticizer used to restore seals and provide flexibility. It is a universal sealer that can treat a range of seals at a low cost.

APT state that this formula will reseal the majority of leaks within 5 hours, which can be very useful for those needing to get back on the road as soon as possible. As a head gasket sealer, it will definitely work but for peace of mind, it is probably worth spending the extra on a formula designed only for blown head gaskets.

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Head Gasket Sealer Buying Guide

Using a sealer to repair your blown head gasket is much more popular in the US than in the UK. This reason is unknown as the statistics are definitely in favor of sealers and it is the fraction of the cost of replacing your head gasket.

A blown head gasket is not just an older car issue, it can happen to any car especially if its not maintained and serviced correctly. White smoke from the exhaust is one of the most common symptoms and you may well see this from many modern cars. Below are some factors to consider before choosing between a head gasket sealer and going all out and replacing the gasket itself.

Symptoms of a Blow Head Gaskets

Deciding when you need to purchase a sealer is dependent upon when you pickup on the fact that their is something wrong. Below is a list of the symptoms of a blown head gasket:

  • White smokes coming from exhaust
  • Engine misfiring
  • White/yellow mixture inside the oil filler cap
  • Engine overheating quickly
  • Fouled spark plugs
  • Coolant leaking below exhaust manifold
  • … and much more

Driving whilst having a blown head gasket certainly is possible but whether you should or not is completely up to you. It is a gamble because the host gases and cold coolant will enhance the problem even further and have potential to warp the metal head. This will result in a much larger bill and could write off the car completely.

Head Gasket Sealer vs Replacement of the Gasket

Although many of the sealer claim to be permanent, it will never match the effectiveness of a brand new head gasket. However, replacing the head gasket is not the cheapest of repairs and is very labor intensive, which makes up the bulk of the expensive bill.

If the cost of the repair is almost to the value of the car, does it even make economical sense to replace the head gasket?

Of course not, using a sealer would be much more cost effective and will allow you to get much more life out of the vehicle before scrapping it. However, if you love your car or it is a collectible, sure go ahead and purchase a new head gasket but it will be expensive if you do not intend on doing it yourself.

Head Gasket Sealers are aimed at car owners looking for a cheap, simple and fast fix so they can get back on the road. If it continues to worsen, it is recommended to get it repaired but many people will use a sealer and not have any issues again.

How to Reduce Head Gasket Problems

As with any component, with age comes issues in terms of the materials breaking down. However, increasing the lifetime of the gasket can be achieved by ensuring your car does not overheat and if it does, switch it off straight away.

Many mechanics even claim ready made solutions are much better than coolant and water mixtures that many people misjudge. You will want to ensure the coolant does not drop below a pH of 7.0 and if it does, refill the reservoir.

How Does a Head Gasket Sealer Work?

A blown head gasket will leave areas where coolant can mix with the engine oil and this is obviously a bad thing. The purpose of a head gasket sealer is to simple locate the areas that will leak and seal them up so no coolant can escape.

They come in the form of a spray (most popular), glue and paste form with many being a permanent solution but this is debatable. Some head gasket sealer may only work for a few years but this would still have been cost effective as you would have had a few years with “gasket-free” troubles.


Coolant leaking everywhere and white exhaust smoke can seem like an expensive repair bill at your local mechanic but do not panic straightaway. Using one of the recommended head gasket sealers above can save you a fair amount of money, which could potential prevent the car being off the road for a long time.

Either the BlueDevil or Bar’s Leak are the most popular products and they are definitely well worth testing before spending thousands changing your head gasket.

procarreviews author

Written By Dan

About the Author

Dan is an automotive journalist and owner of over 10 cars ranging from supercars, tuned cars, classics and your good old beater cars. He always likes to get his hands dirty with nut and bolt restorations or detailing sessions using the best products on the market.

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