How to Diagnose a Head Gasket Leak

Updated April 17, 2017

A failed head gasket is like a heart attack for your car; it can mean the death of your engine if it is not diagnosed in time. The symptoms of a failed head gasket are not always the same since the gasket can fail to the inside, outside or both. Identifying the symptoms of a head gasket leak can help prevent an engine repair from becoming an engine replacement.

Look for white smoke billowing from the exhaust pipe, the most common sign of a head gasket failing to the inside of the engine. Find the quickest place to stop the car when this happens to help minimise engine damage. Check your oil. If coolant is leaking, it the oil will look like light brown sludge. It may be foamy. Your oil level will be high on the dipstick. Do not drive the car any farther.

Look for coolant levels that drop with no spraying liquid or steam under the bonnet. If only small amounts of liquid are passing through the leak at a time, other symptoms may not appear. An overheating car for no apparent cause is a suspect for head gasket failure.

Watch for a lack of power and an engine that is running rough. The loss of compression at the point of the gasket failure will rob your engine of power. The coolant will foul the spark plugs and keep the cylinder from firing correctly. This can occur before other more severe signs are manifested.

Look for a fluid leak where there should not be a leak. Coolant pouring from the side or back of the engine means a bad head gasket. You may see no coolant in the oil because the internal portion of the gasket is still holding. The fluid loss to the outside can be quite significant.

Pull your spark plugs and look for traces of antifreeze on the plug and in the cylinder. By removing the plugs one at a time, you can turn the engine over and watch for a spray of coolant from the spark plug opening. If it happens, you need a new head gasket.

Have the cooling system and the cylinders put through pressure checks if any other signs of head gasket failure are evident. If one or both fail, it is probably a head gasket issue. On older cars, bad valves and rings can give a false reading. The other symptoms will help point you toward the head gasket failure.


This type of repair is best left to the professionals if the head gasket is blown.


Be careful not to breathe the fumes from coolant vapours because they are harmful. Guard against burns from hot metal or hot liquid when checking for a failed head gasket.

Things You'll Need

  • Ratchet and extension
  • Spark plug socket
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About the Author

Allen Teal was first published in 2002 in the "Adult Teacher" and "Adult Student" books for the Assemblies of God Sunday School department. He has also been published on various websites. He received an Associate of Arts in business from Mineral Area College in Park Hills, Mo.