Head gasket
The seal between the two main halves of the engine that keeps combustion, coolant, and oil apart.
In plain English
An engine is built in two main pieces: the block at the bottom, where the pistons move up and down, and the cylinder head bolted on top. The head gasket is a thin seal clamped between them. It holds in the pressure of the fuel burning in each cylinder, and it keeps the coolant (the liquid that carries heat away) and the engine oil in their own separate passages. When it fails, often called a blown head gasket, those three things start leaking into each other or to the outside.
Why it's on your estimate
A shop recommends this repair when testing shows the gasket is no longer sealing. Typical signs are overheating, coolant that keeps dropping with no visible leak, white exhaust smoke that continues after the engine is warm, milky or frothy oil on the dipstick or under the oil cap, bubbles in the coolant, or a rough-running engine. No single sign proves it, and overheating is both a common cause and a common result, so the shop should confirm it with tests.
How urgent is it?
Don't wait
A leaking head gasket does not heal, and driving on it risks severe engine damage, because coolant mixed into the oil stops the oil from protecting the engine and repeated overheating can ruin major parts. It is at its most serious if the temperature gauge is climbing or the oil looks milky; in that case stop driving and ask about having the car towed.
Questions to ask the shop
- What tests did you run to confirm it is the head gasket, such as a check for exhaust gases in the coolant, a compression test, or a cooling system pressure test?
- What caused it to fail, and is that cause being fixed too so it does not happen again?
- Will the cylinder head be checked for warping or cracks while it is off?
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