Cylinder-head gasket
Seals combustion pressure, oil and coolant between the block and head.
Between the cylinder head and engine block.
Its layered sealing surfaces must tolerate temperature changes and combustion loading without connecting adjacent passages.
A precision seal separating several neighboring rooms.
Unexplained coolant loss or combustion gas in coolant needs a controlled diagnosis; residue alone is not proof.
Usually condition-based rather than a routine replacement. Lubrication, overheating and the exact engine affect wear.
Internal-engine work is usually labor-intensive. Diagnosis and the engine code determine the repair scope.
An overheating BMW does not automatically need a head gasket; the cooling fault and sealing must be checked separately.
BMW petrol and diesel engines; petrol-only systems are identified individually.