What are the signs of a blown head gasket?
Common signs of a blown head gasket include losing coolant with no visible leak, white exhaust smoke with a sweet smell, overheating, bubbles in the coolant reservoir, milky residue under the oil filler cap, and rough running. These symptoms can have other causes, so testing is needed to confirm.
Head gasket warning signs
- Coolant level keeps dropping with no visible leak
- White, sweet-smelling exhaust smoke, especially after start-up
- Overheating, particularly under load or on hills
- Bubbles in the coolant reservoir with the engine running
- Milky or mayonnaise-like residue under the oil filler cap
- Misfiring or rough running
What does a head gasket do?
The head gasket seals the join between the engine block and cylinder head. It keeps combustion pressure inside the cylinders and keeps coolant and oil in their own passages. When it fails, these can mix or leak, which leads to overheating and engine damage.
How do we confirm a head gasket failure?
Several faults mimic a head gasket problem, so we test before quoting. Depending on the symptoms, this can include a cooling system pressure test, a combustion gas (block) test on the coolant, and a compression or leak-down test.
What does head gasket replacement involve?
The cylinder head is removed, the head and block surfaces are cleaned and checked for flatness, and the head may be sent for machining if it has warped. A new gasket and head bolts (where required by the manufacturer) are fitted and torqued to specification. The cooling system is refilled and bled, the oil and filter are changed, and the engine is tested. We also fix whatever caused the overheating in the first place.
Questions worth asking your mechanic
Whoever works on your car, these questions help you understand the job and the quote:
- What tests confirmed the head gasket has failed?
- Will the cylinder head be checked for warping or cracks?
- What caused the failure, and has that been fixed too?
- What parts are included — bolts, thermostat, coolant, oil?
From our workshop
Recent jobs photographed at our Sunshine North workshop.
Frequently asked questions
Can I keep driving with a blown head gasket?
It isn't recommended. Continued driving can overheat the engine, contaminate the oil with coolant and damage the bearings, turning a gasket job into an engine replacement.
What causes a head gasket to fail?
Overheating is the most common cause, often from a coolant leak, failed water pump, thermostat or radiator. That's why we look for the underlying cause as well as replacing the gasket.
Do head gasket sealer products work?
They're sometimes used as a temporary measure, but they don't repair the underlying damage and can block other parts of the cooling system. We'd recommend a proper diagnosis first.