How To Tell When Your Head Gasket Is Blown

Diagnosing your Head Gasket is Blown, by looking for the symptoms, can be quite misleading.

This is because a failed head gasket is NOT a single thing. Head gaskets may fail in several different ways.  Many failure types are possible, each with different symptoms.

The symptoms that we may notice will depend on how and where the head gasket fails. Exhaust fumes immediately destroy inhibitors in the coolant, and set up an acid condition.

head gasket blown
head gasket blown

This is bad enough, but the coolant will then conduct electricity, and a galvanizing reaction will begin among the various kinds of metals in the cooling system. This will eat away at the radiator and other parts of the system from the inside. If the coolant should also enter the cylinders (which can happen, but fortunately not often) the result will be a poorly running engine, with less life, and coolant contaminating the engine’s lubricants. Combustion leaks in the valve area force coolant away during heavy acceleration causing excessive heat build-up. When acceleration stops, the diverted coolant rushes back to the area, resulting in internal engine damage.


Adding to the problem of diagnosis may be other factors. For example, a warped or cracked cylinder will produce the exact symptom of a blown head gasket. The best an external inspection can do is determine the problem is head gasket related. This may mean a blown gasket, warped or cracked cylinder head. Removing the head and testing it is the only way to know the extent of the damage.


blown head gasket
blown head gasket

A head gasket that fails between cylinders will generally cause a misfire and perhaps few other symptoms. With a failure between cylinders, compression from one cylinder leaks into another. Lowered compression results in a rough idling engine. Damage of this type may not cause overheating, coolant in the oil or any other outward sign.


Head gaskets may also fail between the coolant passages and the lubrication system. This type failure may show up as oil in the coolant or coolant in the oil. It is also common to find failures between an oil passage and the outside. Such damage results in an external oil leak, and possibly no other symptom.It is also possible for multiple failure types to exist in an engine at the same time.



Cylinder-head surface corrosion is similar to a crack, in the way it affects the gasket. A corroded cylinder head will not allow the gasket to seal.  Such corrosion occurs with improper cooling system service. If the corrosion is severe, we have to replace the cylinder head. With a less serious case, a cylinder head shop can restore the surface with machine work.


Warping is another problem, particularly with aluminum cylinder heads. The surface of a cylinder head may warp and no longer provide a flat surface to hold the head gasket properly. We check a cylinder head for warp, with a straightedge and a feeler blade.  After we remove and clean the head, we use a straightedge and feeler blade to check the surface.  If a problem exists, the feeler blade will pass between the head and the straightedge.
The specification for an allowable warp varies from one engine to another.  The normal limit is .003 to .004 inches for four-cylinder, V6 and V8 engines. With some inline six-cylinder engines the tolerance may be slightly more.  Cylinder head specialty shops may straighten or machine a warped cylinder head to make it usable. They can even sometimes repair cracked cylinder heads.


coolant tester
coolant tester
coolant tester
coolant tester

Works with virtually any liquid-cooled internal combustion engine or generator with a closed cooling system including: gasoline, diesel, propane, natural gas and other alternative fuels. Large, single-chamber design provides greater accuracy and uses less test fluid.

  • Get the engine ready for testing as if you were going to do a compression test.
  • Remove all the spark plugs and Rad Cap.
  • Screw in air line fitting into a spark plug hole and apply full shop air line pressure.
  • Turn the engine over by hand or wrench to make sure all the valves are closed on that cylinder.
  • Once pressure has built up on that cylinder check the rad for air bubbles.
  • Do the same to all other cylinders looking for air bubbles.

If there were no bubbles your OK. If there were you have confirmed a leak


About Danny Bender 106 Articles Is The Premier Automotive Engine Troubleshooting Resource Site. Shares Information On Engine Troubleshooting, Engine Rebuilding, Engine Repair Tips, Tech Info, Basic Machining, Automotive Testing, In addition To Possible Solutions.

13 Trackbacks / Pingbacks

  1. How to find engine coolant leaks
  2. How to find engine coolant leaks
  3. Blown Head Gasket Symptoms-What to look for
  4. How to do a compression test
  5. Radiator cap-What does it do
  6. Antifreeze in Oil - What Can it Do ?
  7. Do you have a Bad radiator cap • Solve Engine Problems
  8. Cylinder Head Gasket Leaks •
  9. PCV Valve (Positive Crankcase Ventilation) -FAQ • Welcome to
  10. Head bolt tips-Never reuse (TTY) head bolts • Welcome to
  11. Original diagnosis problems-Engine or part replacement • Welcome to
  12. Smoking from my car-What does it mean •
  13. How do I Read a spark plug

Leave a Reply