What Is a Head Gasket?

Head Gasket

The cylinder head gasket is an essential component of a fuel engine.

The cylinder head gasket ensures that the pressure created by igniting the fuel vapour through the spark plug stays inside the combustion chamber.

The combustion chamber contains pistons and needs a lot of pressure to make sure the pistons continue to burn correctly.

Additionally, oil and coolant have equally essential tasks, but they cannot be mixed to perform tasks effectively.

The cylinder head gasket keeps the chambers separate to avoid mutual contamination of the fluid.

Besides, to seal the combustion portion of the engine to allow oil and coolant to circulate, the head gasket also seals the engine’s combustion chamber.

This allows the vehicle to fabricate enough power to move forward and prevents harmful gases from escaping from the combustion chamber by directing it through the exhaust system.

The head gasket of modern vehicles is made of several layers of steel material interwoven with elastomer, which makes them more durable.

Vehicles manufactured in the past were fitted with either graphite or asbestos gaskets.

In comparison, today’s head gaskets are better because they are less prone to leaks and pose little to no health risk compared to asbestos gaskets.

Purpose of the Head Gasket

Inside the water-cooled internal combustion engine, three fluids move between the engine block and the cylinder head:

  • Combustion gas (unburned air-fuel mixture and exhaust gas) in each cylinder
  • The water-based refrigerant in refrigerant lines
  • Lubricating oil in oil galleries.

Proper engine operation requires that none of these circuits leaks or lose pressure at the junction of the engine block and cylinder head. The head gasket is a gasket that prevents these leaks and pressure drops.

Types of Head Gaskets

  • Multilayer Steel (MLS): Most modern engines are made with MLS seals. They consist of two to five (usually three) thin layers of steel, interspersed with elastomer. Steaming surfaces are typically coated with a rubber coating, such as Viton, which adheres to the engine block and cylinder head, while the internal layers are optimized for elasticity.
  • Solid Copper: Solid copper foil usually requires a special treatment called an o-ring which places a piece of wire around the bounds of the cylinder to bite into the copper. When this is done, the copper gaskets become very durable.
  • Composite: an older design that is more prone to deflation than newer designs. Composite gaskets have traditionally been made from asbestos or graphite, but asbestos gaskets are becoming less common due to health concerns.
  • Elastomer: uses a steel centre plate with silicone rubber balls to seal in oil and coolant. The holes are closed in the usual way with rolled steel fire rings. This type of head gasket was used in the Rover K series engine.
  • O-ring: these seals are mainly made of steel or copper. They can be reused and, when used between properly prepared flat surfaces, will create the most excellent clamping pressure, due to their significantly smaller area compared to other types of joints.

What Causes a Head Gasket Explosion?

The most repeated cause of cylinder head gasket breakage or damage is usually due to engine overheating.

High engine temperatures are always caused by a lack of coolant inside the radiator, generally due to a leak. Some joints are likely to weaken sooner than others, depending on the material. For example, aluminium expands faster when heated.

Metals that have a higher rate of thermal expansion are more sensitive to heat. Higher temperatures can change the shape of the object, which will cause unfavourable results.

The development and deformation of the cylinder head under the influence of heat weakens its integrity and prevents a good seal of the head gasket.

When the head gasket melts, it is vital to repair it immediately. Continuous inspection of the vehicle with melted gaskets can cause severe and irreparable damage to the engine. Since the gasket is used as a gasket, maintaining pressure is essential for engine power.

Once the seal is broken, it can no longer act as a seal and will allow pressure to escape, drastically reducing engine power – one of the few signs of a broken head. Also, oil and coolant hoses can start to leak where they shouldn’t be.

As coolant enters the combustion chambers, it mixes and dilutes engine oil, reducing the cooling capacity of the cooling system, which can cause the engine to overheat.

Symptoms of a Head Gasket

The engine relies on three essential fluids: fuel, coolant and engine oil. If the seal is broken, all fluids can enter or exit the combustion chamber.

You may notice some or all of the following:

  • Overheating: caused by a lack or reduction of refrigerant. Also caused by the entry of hydrocarbons into the cooling system.
  • White, blue or grey smoke: indicates that refrigerant or oil has entered the combustion chamber.
  • Loss of Power: Due to shortage of compression, which causes splashing, loss of power and reduced fuel efficiency.
  • Colourless Oil: Oil that looks like milk chocolate indicates that the coolant is mixing with the oil in the engine.

Head Gasket Failure

A leaking head gasket often referred to as a “shaped head gasket,” can cause coolant, flue gas, or both to leak. Blue smoke from the exhaust indicates that excess oil is entering the combustion chambers. White smoke from the exhaust means that coolant is entering the combustion chamber.

Head gaskets are classified as external or internal. External leaks are visible as coolant or oil on the outside of the engine (usually at the bottom). An internal leak occurs when fluids enter the second circuit and can cause oil or coolant changes.

The first may be the presence of foam (caused by hydrocarbons) in the coolant expansion tank. A coolant leak in the oil system can result in a mayonnaise-like substance being present in the oil, which can often be seen on the oil filler cap or dipsticks.

However, the existence of this substance is not conclusive evidence of a head gasket malfunction, as the oil could also mix with the coolant in other ways. Besides, the head gasket can fail so that the oil never comes into contact with the coolant.

Therefore, it isn’t possible to definitively determine the condition of the head gasket by inspecting the oil.

Coolant Leakage

If coolant enters the cylinder, combustion of the air-fuel mixture is compromised, reducing engine performance and often causing exhaust gases (white smoke).

This vapour can damage the catalytic converter. If a large quantity of coolant gets into the cylinders, the engine can be hydraulically locked, which can cause severe engine damage.

combustion Gas Leakage

When the combustion gases leave the cylinder, it results in a loss of compression, resulting in a reduced power or improper operation. If combustion gases enter the cooling system, it reduces the efficiency of the cooling system and can cause the engine to overheat.

In other cases, gases can seep into small spaces between the gasket and the cylinder head or engine block which trap these gases and are then released when the engine is stopped. These gases then escape into the refrigerant and create air pockets.

Sometimes these airbags can get stuck in the engine coolant thermostat, causing it to stay closed and cause further overheating, creating more spaces between the gasket and the engine. Otherwise, these airbags can also cause the engine to push the coolant into the expansion tank or to overflow.

Diagnosis and Repair of Head Gaskets

Common methods of testing the head gasket for leaks are a compression test (using a pressure gauge), a leak test, or a chemical test to determine the hydrocarbons in the coolant.

The cost of a replacement component (i.e. the head gasket itself) is usually relatively low, but there are significant labour costs involved in the replacement process. The process of replacing and removing the cylinder head gasket is a tedious task.

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