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Head gasket

Car culture term

Head gasket
Photo: Lewis Collard (Collard) / Wikimedia Commons · CC BY-SA 3.0

What is Head gasket?

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.

Related terms

Timing beltCompression testLeakdown test

Frequently asked questions

How do I know if my head gasket is failing?
Multiple symptoms. White exhaust smoke (coolant burning in cylinders). Coolant in the oil (milky brown contamination on oil cap or dipstick). Misfire or loss of compression (rough running). Sustained overheating that cannot be resolved. Bubbles in the coolant reservoir under load. Any of these symptoms warrants immediate inspection.
How much does a head gasket replacement cost?
Typically $2,000-$4,000 in parts and labor for most engines. Some engines (V6, V8) cost more ($3,000-$6,000). The work requires removing the cylinder head, machining the head if warped, and reassembly. Quality head gaskets are typically Multi-Layer Steel (MLS) gaskets for modern engines. Cheaper composite gaskets exist but are less reliable.
Can a head gasket be repaired cheaply?
Some products claim to seal head gaskets (chemical sealers added to the cooling system). Effectiveness is generally poor; the products are temporary fixes at best. Sustained engine operation with head gasket failure causes more damage. Professional repair is the appropriate solution; chemical sealers should be considered last-resort and typically not effective.
Why are some engines prone to head gasket failure?
Multiple factors. Manufacturing tolerance variation. Specific gasket materials better suited to some engines than others. Engine design (crankshaft and head bolt torque sequences). Temperature management (engines that run hot are more prone). The Subaru EJ 2.5 liter engine had specific tolerance issues that led to documented gasket failure rates. Other engines have been more reliable.
Can I prevent head gasket failure?
Maintain coolant system. Address overheating immediately. Use correct coolant type (mixing wrong types can cause issues). Maintain engine cooling fan and water pump (failures of these cause overheating). Periodic coolant changes per manufacturer schedule. Avoid sustained operation under aggressive conditions if the engine is not built for it. These steps reduce risk but cannot fully eliminate head gasket failure.

Head gasket on the blog

What Made the Ford Focus RS So Special?
What Made the Ford Focus RS So Special?

Ford built the Mk3 Focus RS for just three model years, and people still argue about it. It had 350 horsepower, a trick all-wheel-drive system that could shuffle torque across the rear axle, and a Drift Mode that actually worked. It also had a head gasket problem worth knowing about.

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