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TEST 4: Using A Chemical Block Tester (Combustion Leak Tester)
Some head gasket failures do not show any of the symptoms the previous three tests look for. Yet, the head gasket failure causes the engine to overheat for no apparent reason.
A block test with a block tester is the only way to confirm or disprove that a head gasket failure is causing the overheating issue.
In a nutshell, this is how a block tester works:
- A blue liquid chemical, which is blue in color, is placed in the tester (see photo above).
- The tester assembly is then placed on the open radiator neck (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 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), combustion gases are entering the radiator. This result confirms a head gasket failure, a cracked block, or a cracked cylinder head issue.
- If the blue chemical doesn't change color, you can conclude that you don't have a head gasket failure, a cracked block, or a cracked cylinder head issue.
Where can you get the chemical and block tester? At your local auto parts store or here:
Related Test Articles
There are several more ‘How to test’ articles that I've written that are 3.5L FWD GM specific, that may be of further help. You can find the ones that are located here, at this site, by going to the GM 3.5L Index Of Articles.
If this info saved the day, buy me a beer!
