What the heck is a head gasket, anyway?

When your car's cylinder head is bolted to the top of the engine block, a thin, pre-cut template (usually made of steel plus rubber, Teflon or graphite) is placed between the head and block.
This is the cylinder head gasket. This very sophisticated gasket seals off each of the combustion chambers (cylinders) to prevent any leakage of cylinder combustion or coolant and motor oil that circulate (in separate passages) inside the engine block and cylinder head. A head gasket fails or "blows" when it begins to leak due to cracking, burning, melting or warping. These conditions are often caused by pre-ignition or detonation (pinging), overheating or by improper installation of the gasket or a warped cylinder head or engine block.

The result of a failed head gasket is usually an internal between combustion and coolant areas, but can also be a leak of engine oil. If you catch it early, merely replacing the gasket may solve the problem. But as the leak continues to get worse, bad things can happen to your engine.
If oil should leak into your coolant, this will reduce cooling efficiency and could cause the engine to overheat.

If coolant should leak into a cylinder or into your oil, it could cause rapid engine wear and eventually ruin the engine because the diluted oil will not be able to properly lubricate the moving parts.If one cylinder is leaking compression, this could cause a misfire as well as a dramatic power loss and an increase in your fuel consumption.
If that's not enough, a blown head gasket can also cause damage else-where. For example, if leaking coolant should find its way into the exhaust stream, this might result in permanent damage to your oxygen sensor or catalytic converter.

Much of the cost of replacing a head gasket is for labor, as the engine has to be partially dismantled to get at the gasket. This explains why the cost will vary quite a bit from one vehicle to another.

Unfortunately, some engines are more prone to head gasket failures than others. This is usually due to the design of either the engine or the head gasket. Pre-ignition and detonation are the major cause of headgasket failures between the combustion chamber and the cooling system. Other causes are corrosive (old or rusty) coolant, defective cooling fan or other cooling system defect.

There are several possible warning signs for a failing head gasket. Milky, frothy oil on the dipstick may mean you have coolant leaking into your oil pan. If one spark plug is much cleaner than the rest, you could have coolant leaking into that cylinder.
White exhaust smoke from a fully warmed up engine-- or sweet smelling steam coming out of your tailpipe could also indicate a coolant leak, as would a mysterious loss of coolant, with no visible dripping. Many times you can have a small headgasket leak without any of the above symptoms other than a gradual loss of coolant.

             Signs of a compression leak through the head gasket could be:
     1. Intermittent or constant engine running too hot or overheating
     2. A sudden loss of engine power
     3. Engine coolant that's being forced out of the recovery tank or radiator.
     4.Unexplained coolant loss.
     5. Misfire on cold startup.

The best way to test for a small headgasket leak is a cylinder leakage test at each cylinder.
A compression test will rarely find a headgasket leak unless the leak is so big it is obvious anyway.
Sometimes a leaking intake manifold can mimic a bad headgasket.

Your technician can also test to see if there are any combustion gases present in your radiator, but this test will not always pickup small leaks.

Now then, what about trying a stop leak solution or pellet? In the vast majority of cases, trying to seal the leak in this fashion is a waste of time, and adding foreign substances to your cooling system may tend to clog it up.
However, there are certain engines that come from the manufacturer with a recommendation to use a specific type of sealant pellet as a part of normal cooling system maintenance to prevent the leaks from starting in the first place. This is to compensate for a slight design flaw in the engine.

 

 

Wayne's Garage
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