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Common Causes of a Blown Head Gasket

Dan Ferrell writes about DIY car maintenance and repair. He has certifications in Automation and Control Technology and Technical Writing.

Blown head gasket causes can be varied.

Blown head gasket causes can be varied.

What Causes a Blown Head Gasket?

In general, blown head gasket causes can be divided into four main categories:

  • Overheating
  • Preignition/detonation
  • Hot spots
  • Bad installation

There are several reasons that may lead to any one of these conditions. But recognizing that one or more of them were present before your cylinder head gasket failed will help you find out the root cause and fix the problem to prevent destroying your new gasket. If any one of these conditions is present right now, you may want to make the repair soon and avoid an expensive repair.

A Head Gasket's Tough Job

Of all the gaskets used around your car engine, the head gasket has one of the toughest jobs.

To start with, the gasket has to isolate oil and coolant ports and combustion chambers to prevent internal and external leaks. It also has to withstand extreme temperatures and pressures that are constantly changing. A head gasket has to withstand temperatures that can reach 400°F (204°C) between the cylinder and block, and 2000 to 4000°F (1093 to 2204°C) at the fire ring exposed to the combustion chamber.

Then, besides extreme temperature changes, a head gasket has to resist extreme pressures that go from negative (vacuum) to positive (usually 1000 psi (6895 kPa) or more), as each piston goes through its four-stroke cycle.

On top of that, the head gasket has to fight corrosion and chemicals and withstand the rubbing force from the cylinder head (especially aluminum built ones) expanding as it goes from cold to operating temperature. The gasket does all this while frequently filling minor distortions between the head and block surfaces and vibration during engine operation.

Because of the rough conditions under which it has to work, head gasket construction has improved greatly during the last years to increase clamping pressure and physical resistance.

Even so, a quality head gasket can still yield to extreme rises in temperature or pressure caused by engine performance issues.

This guide examines the reasons behind the main causes that can lead to head gasket failure. Being aware of the different sources of potential issues can help you diagnose the problem(s) that led to a blown head gasket on your particular engine, or keep your gasket from failing in the first place.


I. Common Faults That Can Lead to a Blown Head Gasket

1. Engine Overheating

2. Abnormal Combustion

3. Hot Spots

4. Bad Head Gasket Installation

II. Getting Clues From a Failed Gasket

III. Preventing Head Gasket Failure

IV. Dealing With Potential Head Gasket Failure

Overheating is one of the most common causes of head gasket failure.

Overheating is one of the most common causes of head gasket failure.

I. Common Faults That Can Lead to a Blown Head Gasket

When dealing with a head gasket failure, it is important to identify the root cause behind the failure before installing a new gasket; otherwise, you risk destroying the new gasket.

One or more engine faults can ruin an otherwise perfectly installed, quality head gasket. Therefore, knowing the operating condition prior to a head gasket failure helps you identify the source of the problem and correct it.

The next sections discuss various faulty engine operating conditions and the sources that may lead to those conditions. These conditions are known to cause head gasket issues if not corrected on time. If one or more of these specific conditions were present before your head gasket failed, the sources described in that section may help you diagnose the source of the problem in your vehicle and fix the problem before you drive your vehicle with your new gasket installed. If your head gasket is still good, but one or more of the described conditions is present, you can make the necessary repairs before you end up with a more expensive fix.

1. Engine Overheating

Overheating is perhaps one of the most common causes of head gasket failures. Not only can an overheated engine expose a gasket to temperatures it wasn't made to handle, but it can cause an aluminum head to expand at a greater than its normal rate, crashing the head gasket.

Even if it doesn't destroy the gasket immediately, overheating can weaken a head gasket significantly and cause it to fail soon thereafter.

Some reasons behind engine overheating:

  • Leaking cooling system
  • Failing radiator fan
  • Bad EGR system
  • Clogged radiator
  • Thermostat stuck closed
  • Failed water pump
  • Loose serpentine belt
  • Aged coolant in the system
  • Lack of cooling system maintenance
  • Using the wrong type of coolant
  • Fail to mix antifreeze and water properly
  • Bad radiator cap
  • Failed radiator hose

For more information about the causes of engine overheating, check the post What Causes a Car to Overheat?

Abnormal combustion can also blow a gasket.

Abnormal combustion can also blow a gasket.

2. Abnormal Combustion

Preignition or detonation is perhaps about as common as overheating as a source of head gasket failures.

During normal combustion, the flame that burns the air-fuel mixture in the combustion chamber spreads evenly and smoothly. However, this process can be upset by a lean mixture, overheating, or low-octane fuels.

Abnormal combustion can show as detonation or preignition:

  • Detonation happens when the ignition process in the cylinder develops too slowly, allowing pressure buildup to start a second ignition front at the edge of the mixture that collides against the first combustion process with a loud knock. Engine knock causes internal vibration due to the shock wave that results from the explosion and can lead to physical engine damage, including head gasket failure.

Usually, detonation is produced by:

  • Excessively lean air/fuel mixture
  • Poor fuel distribution inside the cylinder
  • Ignition timing too advanced
  • Failed EGR valve
  • Low octane fuel
  • Preignition, on the other hand, is an ignition process that begins before the spark plug fires. This condition also results in two combustion fronts that collide, producing a pinging sound. Engine pinging is considered a mild form of knocking and is heard as a light tapping noise coming from the engine. Although not as bad as detonation, if engine pinging is left unchecked it can develop into harmful detonation as well.

Preignition is usually caused by:

  • Carbon deposits in the chamber
  • Overheated exhaust valve
  • Glowing spark plug
  • Overheated metal edge
  • Cooling system problems
  • Poor engine lubrication

3. Hot Spots

Cylinder head gasket failure can also be caused by using the wrong gasket for the application.

  • Several vehicle models have suffered from original head gasket failures.

    Some engine designs can lead to hot spots. For example, engines that have exhaust ports that are too close to each other can result in hot spots in those areas.

    This can lead to head gasket failure if the gasket lacks reinforcements in those areas.

  • But it can also happen after having replaced the original head gasket from the factory.

    For example, if the head or the block surface was turned at the machined shop, and you failed to use the proper gasket for the finish, it may cause the gasket to fail.

    Some gaskets are designed to properly fill minor imperfections on the surface they are protecting and can even fill the space taken away at the machine shop. This is designed to prevent upsetting ignition timing, especially on OHC (overhead cam) engines.

    If your block, cylinder head or both need to be resurfaced, make sure to use the correct head gasket for the job.

Always use the right gasket for the application.

Always use the right gasket for the application.

4. Bad Head Gasket Installation

Things can go wrong during the installation process, causing the head gasket to fail. For example:

  • Reusing old head bolts.
  • Using one or more damaged head bolts.
  • Failing to remove dirty spots from the head or block surface prior to installing the new head gasket.
  • Using the wrong tightening sequence or procedure when installing the head bolts.
  • Using sealant incorrectly.
  • Using abrasive pads to clean the head or block cylinder mating surface.
Detonation can cause severe damage to head gasket and pistons.

Detonation can cause severe damage to head gasket and pistons.

II. Getting Clues From a Failed Gasket

When making a repair, studying the old gasket may give you some clues about what went wrong:

Testing for overheating damage:

  • Locate the damaged areas on the old gasket and measure their thickness. You'll need an outside micrometer for this.
  • Measure the thickness of undamaged areas.
  • Compare both measurements.
  • If the damaged areas are thinner than the undamaged areas, more likely overheating or hot spots were the cause of the gasket failure.

Checking for detonation damage:

  • If one or more of the fire rings (gasket rings exposed to the cylinder bores) seem damaged or burned, most likely preignition or detonation caused the gasket to fail.
Prevent engine overheating by keeping the correct level of coolant in the system.

Prevent engine overheating by keeping the correct level of coolant in the system.

III. Preventing Head Gasket Failure

Trying to prevent every instance of potential head gasket failure may be impossible.

Fortunately, there are some common sources of head gasket failures that show up more frequently, that you, as a car owner, may have more control over. Being aware of these engine operating conditions can save you from a head gasket failure and an expensive repair.

Here are some tasks that you can be proactive about to help prevent gasket failure:

  • Whenever you notice the engine beginning to overheat, diagnose the problem as soon as possible and make the necessary repairs.
  • Pop the hood often and check coolant and engine oil levels. If coolant or oil levels drop often, find the source of the leak and make the necessary repairs.
  • Follow your car manufacturer's service recommendations and replace coolant and engine oil as suggested. Consult your car owner's manual or vehicle repair manual.
  • Use only the type of antifreeze and engine oil recommended by your car manufacturer.
  • When you notice a preignition or detonation condition, find out the cause of the problem soon and make the necessary repairs.
Low engine oil level can lead to overheating and head gasket failure.

Low engine oil level can lead to overheating and head gasket failure.

IV. Dealing With Potential Head Gasket Failure

Blown head gasket causes are many and varied. A head gasket failure is an expensive repair to deal with. Not to mention that you won't be able to drive your car for the time being.

If you are dealing with a failed head gasket, make sure to find out the source of the failure before installing the new one to prevent the new head gasket from failing.

Of course, the best way to deal with head gasket failure is to prevent it from happening in the first place.

Unfortunately, there can be many reasons why a head gasket may fail. Modern car engines incorporate many systems, and a fault in more than one of them can have bad consequences for the head gasket. However, you know now about those common conditions that can have an impact on your head gasket.

Be proactive. If your car engine is experiencing one or more faults with similar symptoms to those described here, make the repairs soon to prevent the gasket from failing.

The next video shows you the steps required to gain access to a head gasket on a Honda Accord V6. If you are planning on replacing the head gasket on your vehicle, use the vehicle repair manual for your particular model.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: On an iron block and head combination, is it necessary to re-torque the head bolts? I'm using ARP head bolts. This is a Ford 2.3L turbo engine. Composite gasket (not MLS).

Answer: ARP doesn’t require re-torquing the bolts, unless the head gasket manufacturer instructions says so; also, this is required when installing fire rings.

© 2018 Dan Ferrell