7 Signs of a Blown Head Gasket to Watch For

7 Signs of a Blown Head Gasket to Watch For

If you notice the exhaust of your vehicle is smoky and smells foul, this could be a sign of a blown head gasket. Learn more about this vital engine part and how to check for leaks and other symptoms that could save you trouble and money.

What is a head gasket?

Your engine’s head gasket is a vital seal that connects the cylinder head and the engine block. This metal and composite seal is designed with cylindrical holes to seal the combustion chamber from the oil and water-cooling jackets in the head and block. The combustion, oil and water need to be kept separate by the head gasket or your engine will show clear symptoms of a coming failure.

What is a blown head gasket?

A blown head gasket happens when pressure, usually caused by heat, builds up in the engine, forcing water and oil through a rupture in the gasket seal. This rupture can appear as an internal or external engine leak, resulting in significant and sometimes lasting damage to your engine.

Blown head gasket symptoms to watch out for

A blown head gasket can have multiple symptoms. These are signs to keep an eye on that may help prevent more trouble down the road.

Bubbles in the coolant reservoir

Bubbles that appear in your overflow tank are a troubling sign. Because the cooling system is supposed to be closed, bubbles mean air is coming in. The most likely culprit is a blown head gasket, which allows air from the cylinders to leak into the cooling system.

Unexplained fluid loss

If your car is leaking oil or coolant, there’s a good chance the head gasket has failed. One of the common signs is an external leak at the seam between the engine block and cylinder head.


Another symptom of head gasket failure is cylinder misfires. For example, the failure of a head gasket between a coolant port and cylinder can cause coolant to leak into the combustion chamber. This will often lead to a misfire during ignition after the motor is revved, shut down and restarted.


The less obvious sign of a blown head gasket is overheating. This blown head gasket symptom could be caused by air trapped in the thermostat, which regulates temperature. When the engine overheats, the aluminum head can warp and swell. This causes gaskets and seals to pull away from the metals, leading to leaks.

Loss of power

If you experience a substantial loss of power, it’s another common sign the head gasket has blown. The loss of power is a result of a lack of compression in one or more cylinders because of a failed gasket.

Exhaust smoke

A head gasket leak could also be internal, but you’ll discover it in your exhaust. Oil or water gets into the cylinder through the blown gasket and smoke from the combustion exits through the tailpipe. The smoke will either evaporate into white smoke if it’s coolant or burn into blue smoke if it’s oil.

Milky oil

If you change your oil and it looks like a mocha frappuccino as it drains out, chances are it’s not filled with coffee. This milky substance is oil mixed with coolant seeping past the head gasket and contaminating the engine oil. Make sure to have an expert look at this problem as soon as possible because it could lead to expensive repairs if left untreated.

If you suspect a blown head gasket, you can expect your mechanic to perform two tests on your engine. First, a dry compression and wet compression test will determine if combustion gases are in your cooling system. Then, depending on what the mechanic finds, they may also use a block tester that tests for combustion gases in the engine.

Is it safe to drive with a blown head gasket?

The answer depends on the type of engine and how the gasket fails. You can often drive your vehicle without noticing a problem. For example, if you have a Volkswagen classic air-cooled engine or the gasket fails between cylinders, it may take time before you see symptoms of the failure.

The most significant danger of continuing to drive comes from heat. Because of lost fluids, your engine can get hot enough that the metal will begin to warp and fail. If you don’t notice engine overheating, keep in mind that just because the engine is running OK doesn’t mean everything is good.

That said, if you notice fluid leaks, bubbles in your overflow tank or mixed engine fluids, it doesn’t necessarily mean you have a blown head gasket. It does mean your car might need to be checked soon. The head gasket may not be the first thing a mechanic checks, but it’s still important to have someone look at it.

Delaying a visit to a professional mechanic may risk further engine damage.

Blown head gasket repair cost

A blown head gasket repair is estimated to be between $1,600-$2,000, on average. While the head gasket is relatively inexpensive, the labor costs are estimated to be between $900-$1,200.

Note that other parts may be needed for your engine depending on how long it has been running with the failed gasket. Engine type and size will also cause the cost to vary. For example, an eight-cylinder engine will cost more than a four-cylinder.

Can I repair my head gasket?

Even though a head gasket set can be as low as $45, some can cost as much as $1,300. Buying the head gasket is relatively easy, but repairing a broken head gasket can be complicated, depending on the engine.

You could repair a conventional inline or V-cylinder engines if you’re mechanically inclined and have the special equipment needed. However, it still requires the disassembly of the top part of the engine.

Before removing any parts to get to the cylinder heads, consult a shop manual for your specific engine. Different engines require different tools and procedures. Follow the instructions.

The first step is to remove the intake manifold, fuel lines, hoses and wiring to get to the cylinder head. Do this carefully to prevent damage and label connections to assist in reinstallation.

After removing the cylinder heads, you will see the damaged gasket, cylinders and engine block. First, scrape off the existing gasket and install a new one with a sealant. Replace the parts in the reverse order in which they were removed.

If you take on the challenge of head gasket repair yourself, expect to take a day or a weekend to complete the project. Depending on the car, there’s a lot of stuff in the way that needs to be removed. If you discover there’s a crack in the block or cylinder head, make sure you have a way to get it to a mechanic.

How long do head gaskets last?

There are times when car manufacturers install a bad head gasket and design an unreliable engine. However, if you follow your car’s recommended maintenance, a head gasket will last more than 200,000 miles. As always, driving your vehicle within its limits and properly maintaining it will extend its useful life.

How to avoid a blown head gasket

Heat is your enemy, and the best way to prevent a blown head gasket is to keep the engine coolant and oil at the proper levels and change the engine fluids at recommended intervals.

If you ever notice spots on your driveway, parking spot or garage floor, then have the vehicle checked out as soon as you can. While driving, keep an eye on the temperature gauge. While some temperature fluctuations are normal, a rising engine temperature may indicate more significant issues. It’s best to have the symptom checked immediately by an auto technician.

About Bumper

At Bumper, we are on a mission to bring vehicle history reports and ownership up to speed with modern times. A vehicle is one of the most expensive purchases you'll likely make, and you deserve to have access to the same tools and information the pros use to make the right decisions.

About Steven Mitchell

Steve’s first car had pedals, and he’s been filled with passion for four wheels ever since. Steve lives and breathes the auto industry as a technologist, futurist, and writer while keeping up with the whys, hows, and plans of the automotive industry. His automotive journey began with a fully restored Triumph TR3b that he sadly never appreciated until decades later. Ownership of X-1/9’s, BMW’s, an SVT and a Dodge Ram Hemi have given way to an Audi Sport.

Disclaimer: The above is solely intended for informational purposes and in no way constitutes legal advice or specific recommendations.