2004 Pontiac Bonneville Head Gasket Replacement Cost

Most engines have two major components: the engine block and the cylinder head. These two halves must seal to one another and act as one piece, or the engine will fail. The head gasket is a sealing layer of durable material that is sandwiched between the cylinder head and engine block. When tightened down, the cylinder head crushes the head gasket into the cylinder block, causing any imperfections to be sealed by force.

When the head gasket begins to fail, the engine may have no symptoms at all. They only begin to occur when the leak has reached an engine oil passage, engine coolant passage or the engine cylinder. When that happens, the engine may be very difficult to start, and run roughly when idling. There may be oil or coolant leaking, and the engine may begin to overheat, or at least run hot. At this point, there may be coolant in the engine oil pan — this will look creamy and lighter in color than the oil. Also, the radiator or engine coolant reservoir may have a gurgling sound, the presence engine oil, or smell of combustion. And the check engine light will come on. The coolant being burned in the engine will produce white exhaust that smells sweet, like engine coolant. When the head gasket fails completely, the engine will overheat within minutes of starting, will stall and then won't restart.

Driving with a bad head gasket is hazardous to the engine, and may even be impossible. A failing head gasket typically will lead to your engine overheating and will eventually ruin the engine block, cylinder head, or both. A car with a blown or leaking head gasket should both be towed to a repair facility.

Head gaskets can fail at any time, but they typically last at least 100,000 miles, especially if the oil and coolant are properly maintained. In order to keep the gasket in good condition, dirty or contaminated fluids should be replaced on schedule, and the engine must run at the proper temperature. This is the best way to help prevent head gasket failure, along with avoiding aggressive driving.

In general, there are a few signs that will point to head gasket failure. If engine oil and coolant are found mixed together, either in the engine or in the cooling system, the gasket is often the culprit. Further testing will be done, and a machine shop will try to confirm whether the head gasket is the problem.

Replacing a head gasket is a labor-intensive process and requires disassembly of several under-hood parts before even reaching the engine. Then, parts of the engine will be taken apart in order to inspect and clean the areas touching the head gasket, and to replace the failed gasket. Then everything must be put back together. This process will take several days, typically. If any of the removed components are found to be worn or failing, it may be best to replace them at this time, as well.

If many components are recommended for replacement, or an engine rebuild or replacement is necessary, consider the cost of rebuilding versus getting a new car. Additives that claim to stop leaks or reseal the head gasket from the engine coolant passages are dangerous. They can clog the radiator or damage the water pump.

This is not a DIY project. There's a lot of disassembly to be done, and many factors to consider while repairing a head gasket. If you decide to have the repair done as opposed to getting a new vehicle, it's best to let a professional mechanic.