What Is A Head Gasket In Car and How To Repair It?

What is a Head Gasket in a Car?

Head Gasket is located between the cylinder head and the engine block. This small yet vital component is used to seal the internal combustion process allowing coolant and oil to travel throughout the engine to cool and lubricate.

Which means, that when it “blows,” it could spell big trouble for the engine. Blown head gasket symptoms are pretty easy to identify and need to be rectified pretty quickly to prevent damage to your engine.

In addition to sealing the combustion portion of the engine to allow oil and coolant to circulate, the head gasket also seals the combustion chamber in the engine.

This allows the vehicle to produce enough power to move forward, as well as keep harmful gases from exiting the combustion chamber by directing them through the exhaust system. The head gasket in modern vehicles is comprised of several layers of steel material entwined with elastomer, making them more durable and longer-lasting.

Vehicles produced in the past were equipped with gaskets created with graphite or asbestos. In comparison, today’s gaskets are better as they are less prone to leakage and have little to no health risks as opposed to asbestos-produced gaskets.

The head gasket is a vital component within the combustible engine. The head gasket ensures the pressure created from the spark plugs ignition of fuel vapors remains within the combustion chamber. The combustion chamber contains the pistons and needs a high amount of pressure to ensure the pistons continue to fire appropriately.

Additionally, oil and coolant have equally important jobs but, in order to perform their tasks efficiently, they cannot mix. The head gasket keeps the chambers separated to ensure there is no cross-contamination of fluids.


What Does a Head Gasket Do?

Your car’s engine is divided into two parts, the cylinder block where the pistons and cylinders reside and the cylinder head where the valves, spark plugs, and camshaft(s) are located. Cushioned between these two massive engine parts is the head gasket.

The head gasket plays a crucial role in sealing the engine’s combustion chamber so that your car can build the appropriate compression that is needed to maintain your engine power. It also keeps coolant or oil from leaking anywhere else, preventing your engine from overheating and catching fire.

When the head gasket fails, coolant can get into the combustion chamber and mix in with engine oil, causing significant engine damage.

How Does a Head Gasket Work in a Car?

Comprehending how a head gasket works means first understanding how the engine works as a whole. In the engine block reside pistons that move up and down in cylinders. The pistons are connected to a rotating crankshaft from which your car gets its power. At the top of the engine is the cylinder head where the valves open and close to let the air-fuel mixture in and out of the combustion chamber.

The head gasket ensures the compression generated by the ignition of the air-fuel mixture remains inside the combustion chamber. This allows your engine to operate correctly, thus creating enough power for the car to push forward. Additionally, the head gasket keeps coolant or engine oil from leaking into the cylinders so that your engine runs properly and doesn’t overheat.

Accurate operation of your engine requires that these two fluids don’t leak or mix at the juncture of your cylinder head and engine block. As a seal between these two main engine parts, the head gasket stops the leaks and maintains the pressure.

What Causes a Blown Head Gasket?

Your car’s engine operates in extreme conditions with intense heat. If this heat becomes more than normal, your engine can overheat causing a blown head gasket. The extra heat results in the cylinder head and engine block expanding too much which results in a failure in the head gasket.

Detonation is another cause of head gasket failure because it damages the armors or fire rings, allowing cylinder pressure to leak past the armors.

Because the cylinder head gasket seals coolant passages, a blown head gasket will allow coolant to enter the cylinders. Coolant in the cylinders will cause:

  • White smoke coming from the tailpipe
  • Bubbling in the radiator and coolant reservoir
  • Unexplained coolant loss with no leaks
  • Milky white coloration in the oil
  • Engine overheating

Since the cylinder head gasket also seals in the coolant and oil, you may see streaks of oil and coolant streaming down from the gasket. You may also notice a loss of engine power due to lower cylinder compression if the head gasket leaks to adjacent cylinders.

If you experience any of these symptoms, the cooling system may be pressurized, shut the engine down, and do not attempt to release the pressure. Have your vehicle looked at by your professional technician and always use replacement gaskets that meet or exceed the original manufacturer’s specifications.

5 Symptoms of Head Gasket Blown

Once a head gasket has failed it can cause all manner of problems, including:

1) Overheating

A head gasket failure may have been caused by excessive engine overheating (as a result of a clogged radiator, coolant leak, defective fan, etc.). However, a blown head gasket will also overheat the engine.

Hot exhaust gases can leak into the cooling system, or coolant can leak into the cylinders and be burned as vapor. In either case, the end result is overheating of the engine.

If the car is driven while overheating, the alloy cylinder head can also warp, or steam can damage the catalytic converter, significantly increasing repair costs.

2) Loss Of Power

If the head gasket fails to allow compressed air/fuel to escape, the compression on that cylinder will be reduced. This loss of compression results in rough engine running and a noticeable decrease in engine performance. This type of failure is usually accompanied by noise such as an exhaust leak.

3) Oil Contamination

One of the most common signs of head gasket failure is the milk sludge on the bottom of the oil filler cap or dipstick, sometimes jokingly referred to as a “milkshake”. This is caused by coolant getting into the oil and vice versa.

While this is not conclusive evidence of head gasket failure, it is generally a good indicator and a sure sign that your engine must fall apart in order to find the source of the contamination.

If the oil becomes contaminated with antifreeze, the motor’s bearings are quickly destroyed with every trip. The repair will require at least an engine oil flush, replacement oil filter, and often a complete disassembly of the bottom end of the engine to ensure the bearings are not damaged and to remove any contaminated oil.

4) White Smoke

A faulty head gasket usually results in large clouds of sweet-smelling white smoke coming out of the exhaust. This is caused by antifreeze that gets past the seal into the cylinders and is converted into steam as part of the combustion process.

Less common, but still possible, is a leak from an oil passage to the cylinder, which would cause bluish smoke.

Each of these types of seal failure also allows for combustion pressure in the cooling system or the oil vent system. If a radiator hose suddenly blows its water outlet or the dipstick does not stay in place, this could be the cause.

5) External Leaks

If a head gasket fails between the water or oil passage and the outside of the engine, it can result in a simple coolant or oil leak. This is the least bad version of a blown head gasket, but it’s still serious.

This may not manifest itself as an immediate problem (other than causing a mess), but allowing the coolant level to drop too far can lead to serious engine problems. The other problem is that leaking oil can get into the hot exhaust and lead to acrid smoke and possible fire.

Preventing Head Gasket Failures

A few dollars of prevention is much better than the thousands of dollars cure when it comes to head gaskets. The replacement head gasket itself is inexpensive, but it is very labor-intensive to repair, which significantly increases repair costs, especially for modern cars.

Head gasket failures are usually caused by repeated overheating or by continuing to drive after the vehicle has overheated. The best way to prevent head gasket failure is to make sure that your cooling system is in good working order. And if your car boils over, stop, let it cool down for at least an hour, and then top up the radiator before continuing.

Checking the cooling system is simple: make sure there are no leaks, the radiator is working efficiently, the thermostat opens properly, and the coolant is topped up to the correct level. Also, make sure the fan (mechanical or electrical) is working, has all the blades, and has a cover around it to increase efficiency.

If you suspect head gasket failure, the scientific test is to check the cooling system for combustion gases. This test shows if the compression has gotten into the cooling system and therefore the head gasket has burned out. The old mechanic’s trick is to remove the radiator cap, start the car, and check for bubbles in the coolant.

However, these do not indicate whether there are other imperfections in the head gasket, so the absence of gases in the cooling system does not guarantee a healthy head gasket.

Some older head gaskets can simply fail because they are poorly designed and not tough enough to use. It used to be more of a problem with older metal seals that could only go from cold to hot for so many years before failing.

Fortunately, modern MLS (multiple-layer steel) replacement seals are now available for most applications and offer improved reliability over the original seal design.

How to Replace a Head Gasket?

Replacing the head gasket is not a job for the average DIY enthusiast. While a head gasket leaking due to age is rare, it usually means everything else is worn out by the time it is replaced. If you crack the head off the engine and look inside it may turn out everything else has been fully cooked too.

The best way to prevent head gasket failure is to keep the cooling system in good working order and to make sure the engine is properly tuned and running. The failure of a $ 5 thermostat or $ 3 coolant hose can quickly cause thousands of dollars in engine damage.

How to Change a Head Gasket? – In 6 Easy Step

The following are a few general tips to replace a head gasket. For vehicle-specific head gasket replacement procedures, always consult a service manual.

  • Step 1: Getting down to the head gasket can be an involved process. Always mark and index everything before removal. In this case, it was easier to remove the exhaust manifold, head, and intake as a unit. A service manual is a first and most important tool in the toolbox.
  • Step 2: Check the head and block for flatness. A machined straight edge across the surface and feeler gauge will reveal all. The service manual will provide specifications. Blocks or heads out of specification must be sent out to the machine shop and be repaired. The machine shop will also be able to check for cracks.
  • Step 3: Prepare the surface. Never use anything that will remove metal. Be careful not to scratch the deck of the block or the mounting surface of the head. While it may seem like a good idea to use a scrubber pad connected to a power tool, the surface irregularities created can cause sealing problems down the road.
  • Step 4: Chase the head bolt or stud holes with a tap or thread chaser to remove any crud and prepare the threads. Use compressed air to blow out any stragglers. Correct head bolt torque is of the utmost importance. Any interference can throw off the torque readings.
  • Step 5: Prefit the head gasket in the correct orientation. Never use sealant unless specifically required by the manufacturer. Head gaskets that require sealant will usually come so equipped. The service manual will outline sealant locations and requirements.
  • Step 6: Correct bolt tightening sequence and torque is key to proper head gasket sealing. Use new bolts if required. Coat head bolt threads with some engine oil before installing. Always follow tightening sequence and torque instructions to the last detail.

Why do head gasket repairs cost so much?

The high cost of repairing the head gasket generally results from the labor required to correct the problem rather than the cost of a replacement part. Replacing your head gasket is an extremely time-consuming task as the motorhead must be removed and then replaced.

How Much Does it Cost to Replace a Head Gasket? According to a national average, it costs between $1,624 and $1,979 for a head gasket replacement. The associated labor costs are estimated between $909 and $1147 while the parts themselves vary in the range of $715 and $832.

And the more time a mechanic has to spend on this job rather than anything else, the more they’ll charge you.

Head gasket repairs will cost less if you catch leaks early

The cost of repairing the head gasket ultimately depends on the speed at which the problem is detected. The longer you wait before going to the repair shop, the more you can expect to get back on the road.

Which workshop you choose naturally also affects how much you are likely to pay. While there shouldn’t be too much of a difference in the prices you’re offered, it is probably worth getting a few quotes from local mechanics with Enji so you can be sure you’re getting the best deal.