How to Diagnose Head Gasket Failure

Written by justen everage
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How to Diagnose Head Gasket Failure
Head gaskets can go when an engine overheats. (knuckle image by Witold Krasowski from

A vehicle's head gasket is the thin gasket that seals the space between the engine block and the engine's cylinder head. Head gaskets can become damaged when an engine is allowed to overheat. Most vehicle engines today are designed to run under 121 degrees Celsius. If your vehicle's coolant dips below normal levels, the vehicle may overheat. If the engine is operated above normal temperature, the pressure and heat created can damage the head gasket. Replacement head gaskets usually cost under £65; however, the labour involved in replacing the gasket can be quite expense, usually costing £260 to £520.

Skill level:

Things you need

  • Spark plug socket
  • Ratchet
  • Compression tester

Show MoreHide


  1. 1

    Start your vehicle. Go to the back of the vehicle while it is idling and look at the exhaust pipe. If a large amount of white smoke is coming out from the pipe, you may have a blown head gasket. Smell the smoke to see if it has a burnt odour, as this too will indicate a likely gasket issue. Most vehicles excrete some white steam or smoke, but if the amount that you're seeing seems abnormal, then continue to suspect gasket failure.

    How to Diagnose Head Gasket Failure
    Exhaust Pipe (Motorcycle exhaust image by Crisps 85 from
  2. 2

    Turn your vehicle off and open the bonnet. Locate and remove your oil dipstick, which is marked with the word "Oil." Inspect the colour of the oil on the dipstick. If your see a creamy or light brown colour, continue to suspect the head gasket. If the oil is dark brown (normal) and does not smell burnt, then you may have another issue. The colour change of the oil would be due to water or coolant leaking into the oil during combustion.

  3. 3

    Check the compression of your engine using a compression tester, which can be purchased online for around £26. You will need the specifications for compression for your engine. You can find these specifications in a vehicle repair guide or online. Unplug the wires attached to your distributor to prevent the motor from fully starting. Choose one spark plug to remove and replace with the compression tester hose. Remove the wire from the spark plug. No tools is needed for this, but you may need to tug a little to make the wire release. Try to start your vehicle and check the reading on your tester meter. Release pressure from the hose of the tester by spinning the release valve slowly and remove the hose from your engine. Repeat to test each spark plug socket and record each measurement. If any measurements are below specification, then you have a head gasket problem.

    How to Diagnose Head Gasket Failure
    Spark plug (spark image by Zbigniew Nowak from

Tips and warnings

  • Sometimes, your local auto parts store will allow you to rent tools. Renting, instead of purchasing, a compression tester is sensible because you will probably use it only once.
  • When removing spark plug wires, pull the wire very close to the spark plug end. Pulling on your spark plug wire at a far distance from the plug can result in wire or plug damage.

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