Blown Head Gasket – The Symptoms, Can Be Quite Misleading

Blown Head Gasket - The Symptoms, Can Be Quite Misleading
Blown Head Gasket - The Symptoms, Can Be Quite Misleading

Diagnosing a blown head gasket, just by looking for the symptoms, can be quite misleading.

So, a blown head gasket is NOT a single thing, because it can may fail in several different ways.

As a result, many blown head gasket failure types are possible, each with different symptoms.

The symptoms that we may notice will depend on; how and where the blown head gasket actually leaks. So, exhaust fumes, immediately destroy inhibitors in the coolant, and set up an acid condition.

Blown Head Gasket - Head Gaskets May Fail In Several Different Ways
Blown Head Gasket – Head Gaskets May Fail In Several Different Ways

This is bad enough, but the coolant will then conduct electricity, and a galvanizing reaction will begin. Finally, this will eat away at the radiator and other parts of the system from the inside.

Also, if the coolant should enter the cylinders the result will be, a poorly running engine. Consequently, 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. So, when acceleration stops, the diverted coolant rushes back to that area; resulting in internal engine damage.

Types Of Blown Head Gasket Failures

Adding to the problem of diagnosis there may be other factors. For example, a warped or cracked cylinder, will produce the exact symptom, of a blown head gasket. So, the best an external inspection can do is; determine if the problem is head gasket related.

Cracked Leaking Cylinder Head
Cracked Leaking Cylinder Head

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.

Engine Misfire, Caused By A 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.

Cracked Between Cylinders
Cracked Between Cylinders

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.

Fluid Mixing, Oil In The Coolant And Coolant In The Oil

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.

Head Gasket Leaking Externally
Head Gasket Leaking Externally

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 Corrosion, Caused By A Blown Head Gasket

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, you will have to replace the cylinder head. With a less serious case, a cylinder head shop, can restore the surface with machine work.

Resurfaced Cylinder Heads
Resurfaced Cylinder Heads

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 seal the head gasket. 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. So, if a problem exists, the feeler blade will pass between the head and the straightedge.

Machined Cylinder Head
Machined Cylinder Head

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.

Hydrocarbon, Coolant Testing

Works with virtually any liquid-cooled internal combustion engine, with a closed cooling system. Also, works on, gasoline, diesel, propane, natural gas and other alternative fuels.

Hydrocarbon Coolant Testing
Hydrocarbon Coolant Testing

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.


Prevention is much better than cure, when it comes to head gaskets. A replacement head gasket itself is not too expensive; but, the repair is very labor intensive.

Blown Head Gasket At Fire Ring
Blown Head Gasket At Fire Ring

Above all, head gasket failures are usually the result of an engine overheating. So, the best way to prevent a blown head gasket is to; ensure your cooling system is in good condition.

Ensure the system has no leaks, the radiator is working efficiently; and coolant is topped up to the correct level. Also, make sure the electric fans are working correctly; and that the thermostat opens, at the temperature it should.

Thank You !