Head Gasket Failure: The Signs To Watch For

What a head gasket does

Your engine is built in two main parts: the cylinder block at the bottom and the cylinder head on top. The head gasket is the thin seal between them.

It has a hard job. It has to seal in the pressure of combustion, and keep the coolant and the oil in their own passages so they never mix with each other or end up in the cylinders. When it fails, one of those seals breaks down.

The usual cause: overheating

Head gaskets most often fail after an engine has overheated. The heat can make the cylinder head distort slightly, and the gasket can no longer seal properly.

Overheating usually starts with something smaller, such as a coolant leak, a failed water pump, a stuck thermostat, a broken cooling fan or a blocked radiator. That is why it pays to fix a coolant leak or a rising temperature gauge as soon as you see it.

Check your coolant level every few weeks with the engine cold, using the marks on the expansion tank. If you keep having to top it up, something is wrong, and catching it early is far cheaper than dealing with a failed gasket.

Signs to watch for

The common signs are coolant going down with no leak you can see, the engine running hot or overheating, and white exhaust smoke that keeps going after the engine has warmed up, sometimes with a sweet smell. You might also see bubbles in the coolant expansion tank, or the top hose feeling hard and pressurised.

Other signs include a misfire or rough running, oil leaking from where the head and block meet, and a loss of power. A milky, creamy residue under the oil filler cap gets a lot of attention, but on its own it is not proof. Cars that only do short trips often get some condensation there, especially in winter.

Some of these signs have other causes, so the right thing is to test rather than guess.

If you see the temperature rising

If your temperature gauge climbs or a coolant warning light comes on, pull over when it is safe and switch the engine off. Driving on while overheating is the quickest way to turn a smaller repair into a much bigger one.

Never open the coolant cap while the engine is hot. The system is under pressure and the coolant can be scalding. Let it cool right down first, and then call us.

How we check it

We can pressure test the cooling system to find leaks, and carry out a combustion gas test on the coolant, which shows whether exhaust gases are getting into it. A compression or leak-down test can show which cylinder is affected.

If the head gasket has gone, the repair means taking the cylinder head off. We check the head for flatness and cracks, and it may need skimming flat before it goes back on with a new gasket. We will explain what we find, including whether the repair makes sense for the age and value of your car, and give you a quote before any work starts.

Talk to us early

Mark has more than 30 years in the trade and has seen plenty of engines saved because the owner stopped early. If your car is losing coolant or running hot, call us on 01922 682200 or book online, and we will check it at our garage in Pelsall.