The head gasket is a seal between the engine block and cylinder head that ensures that oil and coolant do not mix, and that combustion stays contained within the combustion chamber.

Symptoms of a blown head gasket can include white exhaust smoke, oil in the coolant or vice versa, loss of coolant without an obvious leak, engine overheating, and low engine compression.

Diagnosing a blown head gasket typically involves a visual inspection of the engine and a pressure test to check for leaks. A mechanic may also use a specialized tool to check for exhaust gases in the coolant, which is a sign of a blown head gasket.

Repairing a blown head gasket typically involves removing the cylinder head and replacing the gasket. The mechanic will also check the cylinder head for warping or other damage and may need to replace other components such as the timing belt or water pump.

The length of time required for head gasket repair can vary depending on the make and model of the vehicle and the extent of the damage. In general, head gasket repair can take anywhere from a few hours to a full day or more.