A Head Gasket is a very important seal in a vehicles engine that sits between the engine block and the cylinder head (this is a machined casting that contains cylindrically bored holes for the pistons) in an internal combustion engine. Today you will find that all cars are equipped with an engine block and a cylinder head that bolts on top.
Head gaskets exist to fill the gap between the cylinder head and the engine block. The head gasket should maintain that seal to be able to avoid leakage between the cylinder head and the engine block while it is under compression. So, therefore its purpose is to seal the cylinders to ensure maximum compression.
To keep within the confines of the engine it is tasked with a few elements - these being:
Oil
Water
Gasoline
Exhaust gases
Now and again the compression in the cylinder may cause a hole that forms in the head gasket. This is known as a blown head gasket. Before the damage to the head gasket can be detected, there are a series of tests that need to be done. The common symptoms of a blown head gasket are:
Foaming
Bubbling
Gargling - all of these 3 will occur in the radiator.
Rapid pressure buildup in the cooling system before the engine has warmed up.
It sometimes also happens when the coolant has spilt over from the reservoir bottle because of the pressure. You may also find other signs for knowing if the head gasket has blown. These will include:
White smoke coming from the tailpipe
Oil in the coolant
Cylinder pressure low when using both the wet or the dry compression method.
If you find that you may be encountering any of these problems, it might be a good time to seriously consider replacing the head gasket. If the head gasket is bad and you just continue to ignore it, the chances are then that your oxygen sensor may have been poisoned at the same time and you will then definitely see the trouble arise.
The problem with a blown head gasket has been exacerbated by the use of aluminum rather than iron cylinder heads. Although it is lighter than iron, the aluminum has a much greater thermal expansion rate. This in turn will cause a great deal more stress to be placed on the head gasket. The manufacturers of engines have responded to this problem by adding a non-stick coating such as Teflon to the surface of the head gasket.
So, if you feel that you may have blown a head gasket, have it checked by a mechanic and you may need it replaced right away.