The head gasket is located between the engine's cylinder head and block. When a spark ignites gasoline in the engine, the explosion creates pressure in the engine. The head gasket provides a seal that keeps that pressure contained within the engine's cylinder. The head gasket also provides a seal for internal engine water and oil passages.
If the engine is allowed to overheat, the cylinder head gasket may become damaged. Running the vehicle when its coolant is low or when there has been a cooling system failure can cause overheating.
Replacing the head gasket requires major engine dismantling. The cooling system is drained, and the intake and exhaust manifolds are removed. The timing cover, timing belt (or timing chain), and valve covers may also need to be removed. In order to gain access to the bolts and hardware securing the cylinder head to the engine block, the camshafts may need to be removed.
After the cylinder head is removed, the cylinder head and engine block surfaces are cleaned and examined for damage. The head gasket is replaced and engine components reassembled.
More Technical Detail
Head gasket failure caused by severe or repeated engine overheating will necessitate close inspection of the cylinder head itself for cracks, as well as measurements taken to assure that the cylinder head is not warped. A warped cylinder head can often be machined flat, but it may have to be replaced.
Due to the damaging effects of coolant entering the combustion chamber, oxygen sensor and/or catalytic converter replacement may be prudent or even necessary. This is especially true if head gasket failure was severe or prolonged.
About this Repair:
Head Gasket(s) Replacement
To prevent an expensive, recurring problem, the integrity of the entire cooling system should be inspected and tested when a head gasket is replaced.
During this repair, the cylinder head(s) will need to be inspected and machined. Additional repairs may be needed after the inspection, which can add several hundred dollars to the repair and are not included in the RepairPal estimate.
Cylinder head gasket replacement often occurs when the engine has high mileage; several additional parts may be needed during the repair. These may include cooling system components (hoses, water pump, radiator, thermostat, etc.) vacuum lines, timing belt, ignition wires, and more. These will be in addition to the RepairPal estimate above.
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 headgasket will often leak engine coolant into the oil, causing a "chocolate milk" like appearance and the oil level my be higher than normal.