What is my headgasket and why did it fail?

Your car's engine is made up of dozens of different metal parts. When they are bolted together, we use gaskets to "seal" the inevitable gaps that occur between these metal parts. Often these metal parts have fluids or gases that flow between them in passageways. The gaskets must keep these fluids or gases from leaking out of their designated passageways.

Your engine has two major metal parts or castings (and many smaller castings). The larger (bottom) part of the engine is called the engine block. It is made out of cast iron. Most engines in the distant past were made entirely out of cast iron.

The second major metal casting is the engine "head" which bolts on top of the engine block. The head on your car, and most engines nowadays, is made out of aluminum. They began using aluminum in the 1970's as a way to make the engines lighter in an effort to increase fuel mileage.

Both the block and the head have many passageways between them that must be sealed by a major gasket called the head gasket.

First, this headgasket must seal the cylinders, where the gasoline is burned at very high temperatures and at very high pressures (1500 degrees is common at 200 pounds per square inch). This burning, or exploding, gasoline makes the power that runs the engine.

These explosions occur in each cylinder at least 800 times per minute when the engine is idling, up to 4000 times per minute when the engine is racing.

Just, a fraction of an inch from these cylinders and this hot exploding gas, are passageways that carry antifreeze and oil. Antifreeze passageways ring the cylinders to help keep the heat from destroying the engine. Engine oil is pumped through passages throughout the engine to lubricate the many moving parts.

The gaskets must keep the antifreeze, oil and compression gases, separated. All these liquids and gases must be kept within their designated passageways even as they flow between the engine block and engine head. The headgasket has quite a job to perform.

Now, the big problem is, as the engine warms up, and cools down, cast iron and aluminum expand and contract at different rates. These castings physically expand and contract, even though they are bolted together. The headgasket must continue to seal the cylinders, the coolant (antifreeze) passageways, and the oil passageways, despite the fact that these metal castings are expanding and contracting. This expanding and contracting is called shearing.

The gasket can handle this shearing so long before it eventually fails. If the gasket fails badly enough (catastrophically), antifreeze in large amounts can enter the cylinders where it is burned and can cause damage to internal engine parts as well as to the car's computer sensors and the catalytic converter in the exhaust system. Now we really have problems. Usually, though, if a headgasket problem is caught early enough, and a proper job is done when replacing it, no major damage will occur.

Neglecting regular maintenance can cause this and other gaskets to fail prematurely.

That is why changing antifreeze every two years is important. It is also why you never want to overheat one of these engines whether it be from a clogged or leaking radiator, a leaking coolant hose, a stuck thermostat, etc.

Many people don't realize that antifreeze, while it is added to the radiator, actually flows from the radiator, through rubber hoses, to the engine, where it is pumped throughout the engine by the waterpump, and by rubber hoses inside the car, under the dash to the heater core (which gives you warm air in the winter) and back through rubber hoses to the radiator, where the entire cycle begins again. Any failure, leak or clog, anywhere in this cycle, can overheat an engine.

If antifreeze is not changed regularly, it becomes acidic, and begins to attack all the rubber and metal parts in this cycle of radiator, hoses, engine parts, heater, etc.

That is why preventive maintenance is so important to the long life of a car.

As for price, there are many places that will quote very low prices to replace a headgasket ($400-500). However, we never quote less than $1000.00-1200.00 for a four-cylinder engine, and $1100.00-$1400.00 for a six or eight -cylinder engine. Turbo charged engines, and engines that are difficult to access, can go much higher. Here is why.

We need to do this job right to avoid having the headgasket fail again in a very short time.

Proper repair requires that the head be removed from the engine to check to make sure it has no cracks and to correct any warpage that has occurred in the head. (The aluminum head can actually warp just like a piece of wood.) Most times the head is sent to a specialized machine shop where these checks are performed, and if the engine has many miles, the machine shop will often perform something called a "valve job" on the head.

We won't go into what a valve job entails. It simply is a good thing to do at higher mileage, but it does add to the cost of the job. We also, remove and service the radiator when doing a headgasket job, just to make sure that the radiator did not cause the engine to run hot, and we also check and replace any of the dozens of coolant hoses that are usually still original. (Hose makers recommend replacing coolant hoses every four years to prevent failures).

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