Your vehicle’s head gasket (HG) is sandwiched between the cylinder head and engine block. The part serves multiple purposes. First, it prevents coolant from seeping into each cylinder’s bore. Second, it helps maintain pressure within the engine by sealing off the combustion chambers. The operation and performance of your car are heavily dependent on the HG’s ability to keep the seal intact and free from leaks.

When the head gasket fails, it must be replaced. Unfortunately, the job is expensive – the price can climb past $1,000. The part itself is relatively inexpensive; a high-quality head gasket typically costs less than $70. The reason replacing it is so costly is due to its location. The mechanic needs to remove the engine head in order to get to it.

Below, you’ll discover the main reasons the HG fails. Some you can avoid while others may be inescapable.

Stress Between Disparate Metals

Your car’s cylinder head and engine block are made from different metals. The heads are usually comprised of aluminum. The block is made from cast iron. One of the reasons cylinder heads are made from aluminum is because the metal is lighter than iron. The problem is, aluminum has a higher thermal expansion rate. When the temperature around your engine rises (as it does during operation), the aluminum expands much more quickly than the block’s iron.

This places stress on the HG. The head and block rub against each other because they are expanding at different rates. Even though the gasket sitting between them is normally designed with steel or copper, the constant rubbing over thousands of miles gradually tears it apart.

Many of today’s vehicles are equipped with HGs made of graphite. This material is more capable of withstanding the stress caused by the varying expansion rates of the cylinder head and engine block. But they can still break down over time.

Bad Installation

There are a few ways in which a bad HG installation can cause problems down the road. One of the most prevalent issues involves the head bolts. These bolts hold the gasket securely to the engine block. If they’re tightened down with the wrong torque, they will create seal problems.

Another issue involves the surface of the block or cylinder head. If either surface is less than smooth, the rubbing between them will accelerate the gasket’s deterioration and eventual failure.

Occasionally, head gasket failure is due to the type of sealer used upon it. If the HG is made from a composite (e.g. graphite), the wrong sealer can cause a chemical reaction. This reaction can degrade the gasket’s integrity.

Stress From Engine Problems

As I mentioned earlier, there are factors that impact your vehicle’s head gasket that you can influence. These involve problems with your engine. The most common engine-related issue that leads to gasket failure is detonation (also known as spark knock). This occurs when the air-fuel mixture within a cylinder’s combustion chamber is poorly calibrated. It can happen due to a malfunctioning exhaust gas recirculation (EGR) valve, bad (i.e. cheap) fuel, and carbon buildup. These circumstances can cause the mixture inside the chamber to ignite erratically, which places stress on the gasket.

Another engine-related problem is overheating (though this is a rarer cause of HG failure than spark knock). Your engine is already operating at high temperatures. When it overheats, the temperature rises dramatically. While the HG is designed to withstand heat, the significant rise can cause it to deteriorate.

There’s obviously very little you can do about the type of metals that comprise your car’s engine block and cylinder head. And you’re unlikely to have much say over the HG’s installation. But you can influence the long-term health of your engine and thereby, help protect the integrity of your vehicle’s head gasket.

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Category: Automotive
Keywords: head gaskets, failing head gaskets, car parts, auto parts