Coolant leaking into the oil system may result in a mayonnaise, or milkshake-like substance in the oil, often to be seen on the dipstick, or oil filler cap. The former may be the presence of foam (caused by hydrocarbons) in the coolant expansion tank. Internal leaks are when the fluids enter another circuit and may result in changes to the coolant or oil. External leaks are visible as oil or coolant on the outside of the engine (typically underneath). Head gasket leaks are classified as either external or internal. White smoke from the exhaust suggests that coolant is entering the combustion chamber. Head gasket with a leak between the rightmost and centre cylinders.Ī leak in the head gasket - often called a 'blown head gasket' - can result in a leak of coolant, the combustion gasses, or both.īlue smoke from the exhaust suggests that excess oil is entering the combustion chambers (although there are other possible causes than a head gasket leak). They are reusable and if used between correctly prepared flat surfaces will yield the highest clamping pressure, due to their much lower surface area compared with other gasket types.

O-ring: these gaskets are typically built from steel or copper.

This type of gasket was used in the Rover K-series engine. The bores are sealed by rolled steel fire rings in a more conventional manner.

Elastomeric: uses a steel core plate with molded in place silicone rubber beads to seal oil and coolant passages.

Asbestos gaskets are increasingly rare due to health concerns. Composite gaskets are traditionally made from asbestos or graphite.

Composite: an older design which is more prone to blowouts than newer designs.

When this is performed copper gaskets are very durable.

Solid copper: a solid sheet of copper, and typically requires special machining called O-ringing that places a piece of wire around the circumference of the cylinder to bite into the copper.

The contact faces are usually coated with a rubber-like coating such as Viton which adheres to the engine block and cylinder head while the inner layers are optimized for resilience. These consist of two to five (typically three) thin layers of steel, interleaved with elastomer.

Multi-Layer Steel (MLS): Most modern engines are produced with MLS gaskets.

The head gasket is the seal that prevents these leaks and pressure losses.

Water-based coolant in the coolant passagesĬorrect operation of the engine requires that each of these circuits do not leak or lose pressure at the junction of the engine block and the cylinder head.

Combustion gases (unburned air/fuel mixture and exhaust gases) in each cylinder.

Within a water-cooled internal combustion engine, there are three fluids which travel between the engine block and the cylinder head:

Engine block seal