A multi-layered steel or composite seal that sits between the engine block and the cylinder head. It contains the immense pressure of combustion while keeping engine oil and coolant from mixing as they flow between the two castings. A failure here allows fluids to cross-contaminate or combustion gases to overpressurize the cooling system.
She's blowing white smoke out the tailpipe, which usually means a blown head gasket.
A blown head gasket often presents as a milky, milkshake-like substance under the oil filler cap or bubbling inside the coolant reservoir.
Related terms
Cylinder head
This cast metal component bolts to the top of the engine block to seal the combustion chambers.
MLS
A type of head gasket constructed from multiple thin layers of steel coated in an elastomer.
Coolant
A fluid circulated through the engine block and radiator to regulate operating temperature.
Engine bay
The engine bay is the structural compartment of a vehicle that houses the motor.