The seal between the engine cylinder head and engine block. Critical for compression and coolant containment. Failure is a major engine repair.
Head gasket is the seal between the engine cylinder head and the engine block. The gasket maintains compression in the cylinders, prevents oil and coolant from mixing, and prevents combustion gases from entering the cooling system. Head gasket failure is one of the most serious engine problems possible, often requiring extensive engine repair or rebuild.
Head gasket failure typically manifests in several ways. White exhaust smoke (coolant being burned in the cylinders). Coolant in the oil (the oil cap or dipstick may show milky brown contamination). Loss of cylinder compression (engine runs poorly or has a misfire). Overheating that cannot be resolved (the gasket failure allows cooling system pressure to escape). Each of these is a serious symptom requiring immediate attention.
Common causes of head gasket failure include sustained engine overheating (the gasket is most vulnerable to overheating), aggressive tuning beyond engine design limits, use of wrong gasket type, or installation errors. The Subaru EJ-series 2.5 liter naturally aspirated engines (older WRX, Outback, Forester) have a documented history of head gasket issues. The MINI N12 and certain other engines also have known issues. Repair typically costs $2,000-$4,000 in parts and labor depending on the engine.