Head gasket replacement

The head gasket seals the joint between the cylinder head and the engine block, keeping the coolant, oil and combustion gases apart.

What head gasket means

When it fails they start mixing. It is a sealed joint deep in the engine, so most of the cost is reaching it rather than the gasket itself.

What the job covers

Head gasket failure diagnosis and combustion test
Cylinder head removal, skimming and refitting
Head bolt renewal
Cooling system flush after repair
Pressure test before return

When you might need it

White steam from the exhaust that does not clear as the engine warms up.
Coolant disappearing with no leak on the ground, or a mayonnaise like deposit under the oil cap.
The engine running hot, or the coolant header tank bubbling.

What it costs, and what changes the price

Typically £600 to £2,000.

Engine layout and whether the head has to be skimmed after removal.
Head bolts are usually single use and are replaced as a matter of course.
If the engine has run hot for a while, other damage may be found once the head is off.

How long it takes

One to two days on most cars.

Common questions

Can it be confirmed without taking the engine apart?

Yes. A combustion gas test on the coolant detects exhaust gases where they should not be, and a pressure test shows where the system is losing pressure.

Are the sealing products in a bottle worth trying?

They can buy time on a very small leak. They are not a repair, and some can block radiators and heater cores.

Why do garages want to skim the head?

Heat can warp the head slightly. Skimming makes the face flat again so the new gasket seals properly.