Head gaskets are the most stressed gaskets in an engine, because they have to deal with multiple tasks at the same time. They simultaneously seal oil, coolant, and engine compression, therefore when they fail, they can fail in a number of different ways. Each failure will result in different symptoms:
This one’s not as easy to spot, especially if the leaking coolant evaporates and leaves little trace of where it is leaking. If a head gasket fails between a waterway and the outside of the engine, coolant will be able to leak out of the cooling system. If the coolant level drops too low the engine will overheat.
If the head gasket fails between the cylinder and an oil gallery it can cause compression to enter the oil system and pressurise the crankcase.
This can in turn compromise the lubrication of vital bearings, such as the crankshaft main bearings.
The same failure will also allow oil to enter the cylinder, where it is burnt off as part of the combustion process. This will cause a drop in engine oil levels, and will also cause blue smoke from the exhaust as the oil is burnt.
If the head gasket fails between an oil gallery and a waterway it will allow the engine oil and coolant to mix. This will result in contaminated oil (the white milky sludge often associated with head gasket failure) and will also compromise the cooling system.
If the gasket fails across the fire rings it can allow the compression to leak from one cylinder to the next. This causes a loss of compression, which results in rough running, misfires, and a loss of power.
This type of failure is not as common as the others, but some engines are prone to the head gasket leaking between the cylinder and the outside of the engine. This allows some of the compression to escape out of the engine, causing a ticking noise at idle, rough running, and a loss of power.
This one is fairly easy to spot, and if the head gasket fails between an oil gallery and the outside of the engine you will be able to see the oil leaking down the engine.
While not as immediately dangerous as other types of head gasket failure it will still require repair as it will only get worse over time. Keep an eye on the engine oil level and don’t let it run low.
If the head gasket fails between the cylinder and a waterway it will allow exhaust gases to enter the cooling system, resulting a pressurised cooling system and overheating.
This, in turn, can result in a damaged radiator, hoses, and other cooling system components.
The same failure will also allow coolant to leak into the cylinder, where it is then burnt off as steam as part of the combustion process. This results in a drop in coolant level, causing overheating.
The steam that is burnt off can also cause lead to damage in the catalytic convertor as it exits through the exhaust system too.