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

Block Tester To Check For a Blown Head Gasket (1995-2000 1.8L Mazda Protegé)

Using a block tester, to test for a blown head gasket, is probably the best test you can perform on your 1.8L Mazda (if TEST 1 thru' TEST 3 don't confirm a blown head gasket but your engine still overheats).

The block test is a very very accurate test and will tell you beyond the shadow of a doubt whether your head gasket is blown or not. You might be wondering why I'm adding this test at the end of this tutorial. Its mainly because a block tester has to be bought or borrowed from your local auto part store.

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 you can buy it here: