How To Test A Blown Head Gasket (1995-1999 GM 3.8L)

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

A combustion leak test (commonly known as a block test) is the go-to test at your local automotive repair shop.

This test will help you determine if you've got a blown head gasket problem on your hands when the previous 3 tests just can't do it.

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 result 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 a cracked cylinder head issue.

You can shop for a block tester here: