Sandwiched in between the cylinder head and block, the head gasket helps prevent coolant from leaking into the cylinder and oil passages. When the head gasket fails, the gradual loss of coolant not only causes the engine to overheat, but it can also contaminate the oil and promote faster wear of rings, pistons and other moving parts. Needless to say, ignoring a bad head gasket is the quickest way to a pretty expensive repair bill.
How Can You Be Sure There's a Head Gasket Problem?
Before you set about having your engine's head gasket fixed, you'll want to make sure you're actually dealing with a bad head gasket. Fortunately, there are several tell-tale signs that indicate a head gasket problem:
Low coolant levels—Noticed how your coolant reservoir always seems to run dry, yet you don't see a single leak anywhere? It's likely because coolant is leaking past the portion of the head gasket that's failed. Just to be sure, you'll want to carefully inspect radiator, water pump, hoses and freeze plugs for any leaks you may have missed.
Coolant in the oil—Pull out your oil dipstick and check the appearance of your engine oil. When coolant intermingles in the oil crankcase, it can give the oil a milky or foamy appearance, usually with a yellowish or brownish color.
White smoke or sweet scent from the exhaust—It's normal to see white smoke from your car's exhaust pipe during startup or near freezing temperatures. However, it's not normal to see it when your engine is at normal operating temperature. If you see large quantities of white smoke on a warm, normal day, then it's likely due to the coolant leaking into the cylinders. The exhaust may also take on a sweet odor when coolant breaches the cylinders.
Overheating—A bad head gasket and the attendant loss of engine coolant can cause engine operating temperatures to climb, eventually resulting in constant overheating issues.
Spark plug misfires—Engine coolant that leaks into the cylinder can also foul the spark plug, causing it to misfire.
Using the Leak Down Test
You can also discover head gasket leaks through the use of a leak down test kit. This usually consists of a specialized pressure gauge and a threaded coupling that connects to the spark plug hole. While the piston is at top dead center, approximately 80 to 90 psi of compressed air is forced into the cylinder.
Engines that are in relatively good condition should show only 5 to 20-percent leakage. If more than 30 percent of the air fed into the cylinder leaks out, then you may have a bad head gasket on your hands.
Is There a Temporary Fix?
There are plenty of products that claim to temporarily or even permanently fix head gasket leaks. Head gasket sealants or "liquid gaskets" accomplish that task by plugging up areas where leaks have occurred, usually with sodium silicate or another chemical with similar plugging capabilities. A liquid gasket could be just the thing to help your vehicle limp home for a few miles or it can even offer a few weeks' reprieve from a visit to the garage.
Head gasket sealants aren't meant to be a permanent fix, however, and they come with their own set of potential problems. For instance, the same sodium silicate that plugs up your leaky gasket could go on to plug up other parts of your cooling system, including the tiny oil and coolant passages throughout your engine's block and heads.
The only way to permanently fix a bad head gasket is to replace the actual head gasket. Unless you have a comprehensive set of tools and the patience to deal with removing the cylinder head and all of its accessories, you're better off letting your automotive repair specialist tackle the job.