Head Gasket Failure: A Broken Parts Perspective

[Counterman]

As an automobile technician, I’m sometimes asked what caused a particular problem to occur. This doesn’t usually happen when the repair surrounds things that most perceive as normal wear items, such as brakes or spark plugs, but when the issue falls out of the ordinary realm, especially for more costly jobs, I can expect the ask.

Head gaskets are one of those jobs, but also one where the answer is not always black and white. An explanation begins with considering the job of a head gasket. A head gasket is responsible for sealing everything that happens between the cylinder head and engine block, including the pressure in the cylinder from compression and combustion, as well as engine coolant and oil as they travel between the head and block.

This is a tall order to begin with, but what makes it even more difficult is thermal expansion and contraction.  The head gasket is sandwiched between two pieces of metal. When they expand and contract as an engine warms and cools, the head gasket is under considerable stress to maintain a seal. When the engine block and heads are made of different materials, such as a cast-iron block and aluminum cylinder head, the different metals expand and contract at different rates, making the job of a head gasket even more difficult.

Since this happens many thousands of times over the life of a vehicle; it’s a wonder that head gaskets last as long as they do. That brings me to my first point. Head gaskets can fail due to age and mileage. Even if a vehicle receives impeccable maintenance and is driven carefully, eventually the head gasket will fail. It’s no different than any other part of a vehicle that wears out over time.

So, age is one of the biggest factors. Period. And there will likely have been some mild symptoms such as a minor coolant loss with no external leaks, or a slightly higher-than-normal engine temperature indicated by the coolant temperature gauge. Unfortunately, these symptoms are rarely noticed or ignored and chalked up to the “old car” excuse.

When the head gasket ultimately fails, the instant result is overheating and rapid loss of coolant, and potentially serious engine damage if the engine isn’t shut down immediately. Because of the sudden nature in which these failures tend to make themselves known, it’s referred to as a “blown” head gasket, as if the failure occurred without any type of warning.

But I can guarantee, as with any type of automotive failure, there was a sign. Believe me. It was just ignored. And that brings me to what is often the coup de gras for a head gasket. Heat. When an engine is overheated, it causes the cylinder head to distort and warp. This can cause the head gasket to fail immediately, (again it’s often the final blow for an aged head gasket) and the typical symptoms are rough running, rapid coolant loss, and thick, white smoke from the tailpipe. The more severe the overheat, the more likely the head gasket, and possible even the cylinder head and block, will be damaged.

Since a head gasket weakens over time, the older the vehicle and the higher the mileage, the more likely it is for overheating to cause immediate head gasket failure. Conversely, a low-mileage newer vehicle can experience mild overheating without causing damage to the head gasket.

The best treatment of any engine is to allow it to warm up fully before driving it aggressively. Much of this is due to proper oil temperature and circulation, but it’s important for the life of the head gasket, as well. The harder you push an engine, i.e. the harder the acceleration, the quicker it heats up. Gentle operation as the engine warms up allows for a more even, controlled distribution of heat in the block and heads, which is easier on the head gasket. Factors such as this can determine head gasket life and are ultimately in the hands of the vehicle owner.

Another factor that leads to the weakening and deterioration of a head gasket is maintenance, or lack of it. The maintenance here would be that of the cooling system. Coolant that is not flushed on a regular basis can become very corrosive, deteriorating system components and elevating engine temperature.

More serious issues, such as severe detonation, also referred to as engine knocking, is another cause, though a less common one. Detonation is when excess heat and pressure cause the air/fuel mixture in the combustion chamber to ignite after the spark plug has fired and combustion has begun.

This creates a very sudden spike of pressure and heat in the combustion chamber, which can cause damage to the head gasket fire ring, as well as internal engine components. This problem is typically caused by too much spark advance, and modern engine management systems prevent this from occurring. However, it becomes commonplace when engines are “tuned” for performance without taking precautions to prevent it or paying attention to symptoms of it.

Replacing a head gasket can be a time-consuming job, and daunting to someone the first time they do it. I mention this because improper cleaning, preparation or installation can lead to early head gasket failure. The critical aspects of head gasket replacement are surface preparation, the condition of the block and head, and the procedures followed.

If the cylinder head or block is warped, they must be resurfaced to ensure a new head gasket will seal. If the machine work isn’t properly done, it can cause the head gasket to fail. Proper cleaning, surface prep, head bolt torque sequence and replacing torque-to-yield fasteners are all aspects of cylinder head installation, that if not properly performed can lead to head
gasket failure.

The longevity of many automotive repairs often falls short of the lifespan of the original component. In the case of a head gasket, a repair that is properly performed with a quality gasket should last as long as the original, but there are many related factors, so you can never lose sight of the big picture of them all.

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