TEST 4: Using A Chemical Block Tester (Combustion Leak Tester)
The block test comes in handy when the 3 previous tests can not confirm that a blown head gasket is causing the engine to overheat as it runs.
To be a bit more specific, the engine in your 2.2L Isuzu Amigo or Rodeo starts and runs, but it starts to overheat within a few minutes. Everything is working (like water pump, radiator cooling fan, etc.) and yet the engine overheats. It's in these cases that a block test can pinpoint the problem to a blown head gasket.
For the most part, it's the go-to test performed in an automotive repair shop when they diagnose a blown head gasket.
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 coolant filler neck or coolant tank (you may have to drain some of the coolant in the radiator since this tool needs to ‘gulp’ some of the air inside the coolant filler neck or coolant tank).
- The rubber bellow is then squeezed to suck the air into 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 thus confirming that the head gasket is blown.
- If the blue chemical doesn't change color, then you can conclude that you don't have a blown head gasket, a cracked blocked, or a cracked cylinder head issue.
Where can you get the chemical and block tester? At your local auto parts store or here:
If this info really saved the day, buy me a beer!