Head Gasket Basics

What is a head gasket, and how does it blow?

In my last article I discussed a recent trip to the high country, where a mate’s Patrol overheated and blew its head gasket. The owner of the Patrol decided to fix it himself the following weekend. While fixing his car, he had a few questions as to what a head gasket actually is and how it blows.
The cylinder head gasket is the seal that joins the cylinder head to the engine block. It plays a very important role in the engine as it seals a number of different passages, as well as the combustion chambers.

Manifold and rocker cover off; the cylinder head with all parts removed, it will be ready for reassembly after a quick clean.


Manifold and rocker cover off; the cylinder head with all parts removed, it will be ready for reassembly after a quick clean.

An engine needs oil to flow through it for lubrication, water to flow around it for cooling, combustion chambers for the ignition of the fuel-air mixture, and bolts to hold it down.
So the head gasket serves a complicated role – it not only has to be able to cope with a pressurized cooling system and a pressurized oil system, but it also has to be able to cope with extreme combustion pressures and temperatures.
It's important to remember that the most common cause of a blown cylinder head gasket is due to an engine overheating. The cylinder head on most modern vehicles is made from aluminium, and when the engine overheats the head gasket can become damaged, and in a lot of cases the cylinder head itself can bend or warp, which causes it to pull away from the gasket.
It is possible for the gasket itself to deteriorate over time, which can also cause the fault. When the gasket blows, it causes the passages to mix and in most cases will cause the combustion chamber to mix with the water passages.

The cylinder head gasket, each passage marries up to the passages within the engine block and cylinder head.


the cylinder head gasket, each passage marries up to the passages within the engine block and cylinder head.

Repairing a blown head gasket is quite a big job. It requires the removal of the entire top end of the engine, and it doesn’t stop there. The cylinder head will need to be sent to a head engineer where it will be checked for straightness and cracks, and the valves and valve guides checked and re-seated, among other things.
The cause of the overheating will also need to be attended to. This may be as simple as a leaking hose, or it could be a faulty water pump or thermostat. The radiator should also be checked for leaks and blockages as well. The last thing you want is to have all this work done and find that the engine overheats and blows again because the simple checks were not carried out.
Being vigilant in checking your water levels and watching your temperature gauges could very well prevent a major repair like this. Picking up a small problem before it becomes a big one is always the best method!
Hope to see you all out there.
GO NUTS!

 


Qualified motor mechanic Adam Adler has spent half his life under the bonnet of a 4WD and has worked for some of the top accessory companies and workshops. He knows what it takes to get your vehicle out there and back home in one piece. He runs the online aftermarket store www.nutsabout4wd.com.au.

 


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