How To Test A Blown Head Gasket (3.4L V6 Chevrolet, Pontiac)

TEST 4: Using A Chemical Block Tester (Combustion Leak Tester)

The majority of head gasket failures can be correctly diagnosed with the previous three tests, but there are some cases where those same three tests cannot confirm or exonerate a head gasket failure.

In these cases, the engine starts and runs, but overheats within minutes. No matter what gets replaced, the overheating problem does not get resolved.

The only way to pinpoint the issue to a head gasket failure is by doing a combustion leak detector test (more commonly known as a block test).

This is how the combustion leak detector test (block test) works:

• The combustion leak detector tester is filled with a blue liquid chemical (see photo above).
• The radiator cap is removed (you may have to drain some of the coolant in the radiator since this tool needs to ‘gulp’ some of the air inside the radiator).
• The engine is started.
• The tester is then placed on the open radiator neck.
• The rubber bellow is then squeezed to suck in the air up through the two fluid-filled chambers. As the air bubbles up through the fluid, it will cause a chemical reaction.
• If the blue chemical turns yellow (for gasoline engines), then combustion gases are entering the radiator. This in turn confirms a blown head gasket, a cracked block, or a cracked cylinder head issue.
• If the blue chemical doesn't change color, then you can conclude that you don't have a blown head gasket, a cracked block, or cracked cylinder head issue.

You can shop for a block tester here: