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

Block Tester To Check For a Blown Head Gasket

There are times a head gasket is hard to diagnose as being blown (and behind the overheating issue you're trying to resolve). In cases like these, only a block test will confirm or exonerate the head gasket as blown.

In a nutshell, this is how a block tester works:

  1. A blue liquid chemical, which is blue in color, is placed in the tester (see photo above).
  2. 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).
  3. 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.
  4. If the blue chemical turns yellow (for gasoline engines), then combustion gases are entering the radiator thus confirming a head gasket, a cracked blocked, or cracked cylinder head issue.
  5. If the blue chemical doesn't change color, then you can conclude that you don't a head gasket, a cracked blocked, or cracked cylinder head issue.

Where can you get the chemical and block tester? At your local auto parts store or here:

More 2.0L Mazda Tutorials

There are several more ‘How to Test’ articles that I've written that are 2.0L Mazda specific, that may be of further help. You can find the ones that are located here, at this site, by going to the Mazda 2.0L Index of Articles.

Here's a small sample of the tutorials you'll find in the index:

  1. How To Test The TPS (1994-2002 2.0L Mazda 626).
  2. How To Test The MAF Sensor (1996-1997 2.0L Mazda 626).
  3. How To Test The Fuel Pump (1994-1999 2.0L Mazda 626).