What Causes a Blown Head Gasket? 


The most common cause of a blown head gasket is engine overheating. The cause of a blown head gasket can also be due to a manufacturing defect or just high mileage. Some car engines were poorly designed where the head gasket fails from normal operation and not due to any other causes.



Common signs that you have a blown head gasket include:

Engine overheating

  • blown head gasket engine overheatingOverheating can be caused by a blown head gasket. The engine’s heat can get so high that it melts the head gasket, deforms the cylinder head, and can also cause a crack in the engine block. This causes the coolant to leak into the combustion chamber or mix with oil. When this happens, you lose coolant. The engine won’t cool down if there is no more coolant in the engine.  Just like a blown head gasket can cause overheating, overheating can also blow your head gasket.

Low coolant

  • When the head gasket fails, it will allow the coolant to escape once the engine gets hot. Therefore if you are adding coolant constantly, there is a good chance that you have a blown head gasket.

Bubbles in the radiator

  • You will notice bubbles if you remove the radiator cap (only at startup, never when the engine is hot). If the engine is hot, don’t remove the radiator cap, or you will get burned by the hot coolant. Instead, you can use caution, remove the overflow reservoir cap, and check for bubbles there. That’s safer than removing the radiator cap when the engine is hot.

Milky oil color

  • A blown head gasket allows coolant to mix with oil, causing the oil to look milky. If you check the oil, you will find that the oil is milky or white-looking in color. Check the oil via the dipstick and not by looking at the oil cap. Due to condensation mixing with oil at the cap, vehicles that make short trips will often have white oil under the oil. Water and oil mixing under the oil cap don’t always mean the head gasket is blown.

coolant antifreeze in the radiator white milky oil

You can still have a blown head gasket but no evidence of coolant mixing with oil or the “milky” white oil. That’s because the head gasket can fail in a way that only allows the coolant to get into the combustion chamber, leak to the outside of the engine, and never mix with oil.

Other symptoms of a bad head gasket include the rough idle and no start or intermittent starting.

Just because you are experiencing one or two of these symptoms doesn’t necessarily mean that you have a blown head gasket, as there could be other problems causing similar symptoms.

Before you decide to replace the head gasket, it is important to perform proper testing. Do a compression test or have an auto mechanic diagnose the problem.

How to Check for a Blown Head Gasket

You can’t diagnose a bad head gasket by looking at the head gasket unless you remove the cylinder head. There are easier and better ways to check for a blown head gasket.

Check Coolant

One of the easiest ways to check for a blown head gasket is to turn on a flashlight and point it at the coolant overflow reservoir. Do you see any bubbles?

Watch this video to see it in action. Yes, that is a blown head gasket.

You can perform a few other checks without any tools to see if you blew your head gasket. If you aren’t sure if the head gasket is blown, you can perform pressure testing using an Engine Pressure Test Gauge, which we will discuss below.

To verify that you have a blown head gasket, we first look at the symptoms to see if you are experiencing two or more.

Check for bubbles in the radiator.

Let the engine cool down completely only if the engine is cold open the radiator. Do not open the radiator cap if the engine is still hot. Startup the engine and rev up the engine to 1500 RPMs. Do you see any bubbles coming up?

Check exhaust

If the coolant is getting into the combustion chamber due to a blown head gasket, it will burn with the gasoline and cause the exhaust gases to have a white color and an unusual “sweet” smell.

Check oil color

check oil color to determine head gasket

Next, we need to check the oil color. If the oil is white instead of normal or dark, it means that you may have a blown head gasket. If the oil color is normal, continue to the next step to verify if you have a blown head gasket.

Let’s say you followed the above steps and discovered that you have one or two of the symptoms. Let the engine cool down. Once the engine has cooled down, remove the radiator cap and add 50/50 antifreeze.

Don’t add just water, as this would make diagnosing a blown head gasket problem even more difficult. Water has a boiling point of 100 Celsius, and once the engine reaches operating temperature, the water will want to turn into steam. It will create excessive pressure in the cooling system and maybe even escape through the overflow tank.

Fill the radiator with coolant. Give it a minute and top off again with coolant. Start the car and run it idle for about twenty minutes.  During this time, monitor the temperature on your instrument cluster. If the engine starts to overheat, turn it off and terminate this test.  Your temperature should go past the middle mark, and you should not get the temperature to overheat symbol in the instrument cluster.

Perform a radiator coolant test

Everything so far is leading you to believe that you have a blown head gasket. Let’s not rush to that conclusion yet. It could be that you have a stuck thermostat or the radiator cooling fans aren’t working.

We want to be sure that you definitively have a blown head gasket. One of the cheapest ways to check if you have a blown head gasket is to use a combustion test kit.

Perform Compressor test

A combustion test kit should give you a good idea if the head gasket is blown. If you still aren’t sure or don’t want to perform this test, you can perform a compression test.

compression text for head gasket overheating

To perform a compression test, you will need a compression test gauge. You will need to remove the engine cover, which is easy, the ignition coils, and the spark plugs.

Install the gauge into the spark plug hole and see what pressure reading you get. A healthy engine should get a pressure reading of over 100 psi in all cylinders.

If you have pressure under 100 psi, you most likely have a blown head gasket. You may also have a blown head gasket if the pressure difference between two cylinders varies significantly by more than 10 PSI.

If the head gasket hasn’t failed near the cylinders, but in other parts, you may get good compression but yet notice oil mixing with antifreeze.

If your check engine light is on, make sure to read the codes and address them as well. In a few cases, an engine with timing problems may be advanced too much to the point that the valves don’t fully close when the piston reaches the top dead center (TDC). Not very common, but it’s important to keep in mind.

Can I use a sealer to fix my blown head gasket?

blown head gasket additive

The Head gasket sealer may be able to fix a blown head gasket temporarily. There are many DIY head gasket sealer kits out there. Keep in mind that If the head gasket is damaged beyond repair, no head gasket sealer will be able to fix it.

Two of the best-rated head gaskets kits are:

The BlueDevil head gasket sealer has been around for a long time, and if you do a quick search, you will find many positive reviews about it. Note that the BlueDevil head gasket sealer requires removing the thermostat and completely flushing the cooling system.

Bars head gasket fix is also an excellent head gasket sealer. It has many positive reviews and, most importantly, doesn’t require the thermostat to be removed or the cooling system to be flushed. It is important to realize that the earlier you address the overheating issue, the higher your chance of the head gasket sealer working.

Do head gasket repair additives work?

Note that there is no guarantee of how long a head gasket sealer will last. Such a fix could last a week, or it can last several years. In our opinion, a DIY head gasket fix is still worth trying since a bottle of BlueDevil or Bar’s Leaks Fix is a lot cheaper than replacing the head gasket.

Don’t expect a head gasket sealer to work every single time. Often car owners wait too long before they try a head gasket sealer, at which point the damage is non-reservable, the cylinder head has warped, or the engine block has cracked.

How much does it cost to repair a blown head gasket?

The typical cost to fix a blown head gasket varies from $1000-$1300. The actual price to repair a blown head gasket varies by make and model and the hours required to replace the head gasket.

Repairing the head gasket on certain vehicles may cost as much as $5,000 or $6,000. Don’t be shocked if you got a ridiculous expensive quote for a head gasket repair. Replacing the head gasket is a very labor-intensive job.

The head gasket part is cheap and usually only costs between $100 and $300. Replacing the head gasket can take anywhere from 5 hours to 20 hours of labor or even more. In some cases, with V6, V8, and V12, the engine may need to be removed from the engine bay to repair the head gasket. That’s why you notice that many mechanics in your don’t even want to do a head gasket repair.

They won’t tell you that directly, but once you ask when they get to repair your head gasket, they will often say they are too busy at the moment or are booked for several weeks. Replacing the head gasket yourself will cost you around $200 to $400. Replacing the head gasket would be considered a difficult job.

Six and eight-cylinder engines are more difficult than four-cylinder engines. A skilled home mechanic should change the head gasket within a couple of days if you have the right tools.

Make sure you have a shop repair manual on how to change the head gasket on your car. In some cases, it may make more sense to completely replace the engine with a used engine instead of trying to repair the blown head gasket.

Can you drive with a blown head gasket?

It is NOT recommended to drive with a blown head gasket unless you know exactly how the head gasket has failed. If it only allows oil and coolant to leak from the engine to the exterior, you can drive it as long as you keep topping those fluids daily. You shouldn’t drive the car if the failure is between oil, coolant passages, and the combustion chamber.

Do not drive a car that has a blown head gasket and is overheating. You will cause more damage to the engine to the point that it may become dangerous or the engine can seize up. If you have a blown head gasket, you may ask yourself how long your car will last with a blown head gasket.

If you drive a car with a blown head gasket, you may have a running car for only a few more minutes. Stop driving a car if you think it has a blown head gasket.

Is a blown head gasket worth fixing?

You must consider your options if your car has been diagnosed with a blown head gasket. If you got a quote to get it repaired for $800-$1200, you might have to bite the bullet and get it fixed if your car is worth several thousand dollars.

If the quote is over $2000, consider replacing the engine with a used one. Typically you can find a used engine for around 500-1000; check prices on a used engine.

If you have an older car diagnosed with a blown head gasket, in some cases, it may not be worth fixing. The cost of head gasket repair may be much higher than the price of the car itself. A head gasket sealer may be your only hope but don’t expect it to work miracles every time or last forever.


A blown head gasket can be difficult to diagnose and even harder to repair. The symptoms of a blown head gasket vary and aren’t always the same. You may notice the loss of power. You may have a blown head gasket but not realize it as there is no coolant mixing with oil or leaking oil.

You may have a blown head gasket between cylinders, which could be hard to diagnose, and the only symptoms may be an engine misfire.

The head gasket may fail so that the engine turns over, but it won’t start or struggles to start. A blown head gasket can keep your car from starting. When you have a blown head gasket, you may have no heat, no white smoke, no start, no check engine light, or even no overheating in some cases. Get a second opinion from your auto mechanic or dealer if you are in doubt.

We hope you find the What Causes a Blown Head Gasket guide helpful. Check these troubleshooting and repair guides for more help on your vehicle.

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