Cylinder head gasket problems: how to tell if it has blown or is in poor condition?

You’ve surely heard of it: the cylinder head gasket. And you’ve probably also shuddered at the thought of having problems with this part, since a faulty one can cause a serious engine failure in your car. Today we’re going to learn a little more about the famous cylinder head gasket: what its role is, which symptoms can warn us of a possible cylinder head gasket failure, what maintenance it requires and how much it costs to replace it.

What is the cylinder head gasket in a car engine and what is its function?

The cylinder head gasket is the part fitted between the engine block and the cylinder head. Its main job is to provide a seal, not only to ensure the combustion chamber is airtight during compression, but also for the cooling and lubrication systems, preventing the coolant from coming into contact with the engine oil.

Because it is subjected to very high temperatures (which differ between the block and the cylinder head itself) and to extremely high pressures, it has to be strong but at the same time offer a certain degree of elasticity, so that it can allow the block and head to join and seal, and absorb the expansion that occurs when the engine reaches its operating temperature.

There are different types of gaskets, depending on the material they are made from. They are usually made of a stainless steel sheet and one or more fibre layers, with metal rings around the cylinder bores and around the holes for the various passages, to withstand the sealing pressures. There are also aluminium and copper gaskets, steel gaskets, metal-coated composite gaskets, and so on.

Each engine must use a specific gasket, not only because of the different channels for cooling and lubrication or the bolts that join the head to the block, but also depending on the material the latter are made from. A gasket for joining an aluminium block and an aluminium head is not the same as one for a cast iron block and an aluminium head, for example.

What are the symptoms that our engine has cylinder head gasket problems?

Normally the cylinder head gasket needs no maintenance or replacement and can last the entire life of the car. But there are problems that can cause this gasket to deteriorate, which in turn can lead to bigger failures. That is why it is important to know the different symptoms that can serve as clues to detect cylinder head gasket problems. These include the following:

• High engine temperature. Overheating is one of the first reasons a cylinder head gasket tends to fail. This problem can cause the coolant level to drop and require frequent topping up.
• Excessive pressure in the cooling system. The circuit hoses build up a lot of pressure, to the point that they can burst.
• High consumption of water or oil. If the car suddenly starts consuming oil or coolant, it is a clear sign that the cylinder head gasket may be damaged.
• White or grey smoke from the exhaust system. This is due to coolant or oil entering the cylinders, because the gasket no longer performs its job of keeping the seal.
• Brown-coloured coolant, as oil gets into the cooling circuit.
• Rising oil level, due to coolant being present in the lubrication system.

How much does it cost to replace the cylinder head gasket?

Although the part itself is not expensive (a cylinder head gasket for a conventional 4-cylinder engine can cost between 30 and 50 euros), a blown cylinder head gasket is an expensive failure, since replacing it requires separating the cylinder head from the engine, with the corresponding labour. The average price can be around 500–800 euros, including the part and labour. Bear in mind that the oil and coolant will also need to be replaced.

Even so, if the failure is detected in time, replacing the gasket is always much cheaper than the damage that may result if we keep driving. For example, if overheating has occurred, it may be necessary to replace the cylinder head completely, or carry out a process called skimming, which removes a thin layer of material from the head and/or block to eliminate the distortion that would make it impossible to achieve a perfect seal when they are joined again.

In this case of a cylinder head gasket change that requires skimming, between the preliminary inspection, the labour for resurfacing the cylinder head (and usually the valve seats too), the new bolts, etc., the repair can cost between 1,500 and 2,000 euros.

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