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Don’t Blow a Gasket

You see billowing clouds of white smoke coming out the tailpipe. Or maybe there is a large puddle of black oil or red transmission fluid under the vehicle. In the first case, you more than likely have blown a head gasket that needs immediate attention.

Cylinder head gasket failures allow coolant to leak into one or more cylinders where it boils and turns to steam, hence the reason for the white cloud. Coolant in the oil reduces the oil’s lubricating properties leading to accelerated wear as pistons move up and down. Repair of other leaks are less urgent, if you do not mind cleaning up a mess. However, it very important to keep the source of the leaking fluid - crankcase, transmission, master cylinder or power steering pump reservoir -- topped off with the proper fluid.

Head gaskets have a tough assignment. They have to seal the combustion chambers from loss of very high temperature exhaust gases while preventing leakage of coolant and oil into the combustion chambers. Head gaskets must provide a leak-free seal for the life of the engine and do it from the time the engine is started for the first time.

One symptom of a head gasket failure is bubbles in the coolant when you remove the radiator cap (the one on the radiator and the not the coolant reservoir) and look in with the engine running. Bubbles in the radiator could also mean a cracked cylinder head or cracked cylinder wall. Other symptoms of a bad head gasket include oil in the coolant or coolant in the oil, loss of power and of course, white smoke out the tailpipe.

If you suspect a defective head gasket, you can perform leakdown test. If you want to do itself, you will need a leak down tester and a source of compressed air. You can either buy a relatively inexpensive leak down tester ($60-100) or rent one from a tool rental center. You will need a source of compressed air to operate the tester.

There are three basic reasons for cylinder head gasket failures:

  1. Poor engine design
  2. Improper gasket installation
  3. An overheated engine
  4. .

Vehicle owners really only have control over the third reason for gasket failures. Not only must a bad head gasket be replaced immediately, but more importantly the cause of the overheating must be diagnosed and corrected to prevent a future failure. Check for the most obvious overheating problems first. These includes proper functioning of the radiator, thermostat, water pump, cooling fan, and so forth.

One of the biggest causes of overheating is a dirty cooling system. As little as 1/8 inch of deposits in a radiator may reduce cooling efficiency by 40-percent. It’s also important to use the correct type of coolant and the proper mixture. If these all check out, overheating could be caused by abnormal ignition, such as pre-ignition and detonation which can usually corrected by a tune-up to specifications.

Besides blown head gaskets, overheating can lead to warped cylinder heads adding to repair costs since. At best warped heads have to be resurfaced, and at the worst, they must be replaced. Compared to the old all-iron engines, today’s all-aluminum, and especially bi-metal (aluminum and iron) engines are more prone to gasket failures. This occurs because iron is more durable than aluminum, and iron expands at only about half the rate of aluminum. Thus when a bi-metal engine overheats, the likelihood of warpage and gasket failure is much greater than with all-iron and all-aluminum engines.

Besides head gaskets, other gaskets are used as interfaces between engine components like the oil pan, valve covers, water pump, timing chain cover, intake and exhaust manifolds, etc. Gaskets and seals are also found in the fuel, air-conditioning, and braking systems. Transmissions have many gaskets and seals.

Because of the different fluids involved - oil, engine coolant, fuel, air, hydraulic brake fluid, a/c refrigerant and automatic transmission fluid - each with their own characteristics - it critical that the correct gasket or seal be used whenever a component is repaired or replaced. Unless a seal or gasket is made to be reused, always install a new and correct one. Before reinstalling reusable ones, clean and carefully inspect for damage before reinstalling.

Sometimes, a leaking gasket in a low pressure situation, such as a valve cover, can be cured by tightening the cover bolts or screws, but cure may be only be temporary and the gasket may have to be replaced.

Speaking of retightening, if the cylinder head requires re-torquing after so many miles of running after a new head gasket has been installed, make sure it gets done and done properly, that is, according to the service manual or manufacturer’s recommendation for the particular engine.

Finally, if the automatic transmission is leaking, try using a high quality sealer designed specifically for automatic transmissions before investing in a rebuild. There are several good products on the market. These are designed to keep seals soft and pliable a well as stop leaks caused by drying, hardening or shrinking of transmission seals, a frequent problem with vehicles that sit idle for an extended period, such as when they are in storage.