1999 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.

Head gasket failures are often due to an overheated engine, but can also be caused by high mileage and/or age.

An early sign of a failing head gasket will be a rough running engine when you first start the vehicle, especially if it's been sitting overnight. The rough running will generally last for only a few seconds.

A leaking head gasket or cracked cylinder head will often leak engine coolant into the oil, causing a "chocolate milk" like appearance and the oil level may be higher than normal.

Failed head gaskets or damaged cylinder heads can cause engine coolant to leak into the combustion chamber, producing a white, sweet-smelling smoke from the tail pipe.

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.