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

Using A Chemical Block Tester (Combustion Leak Tester). How To Test For A Blown Head Gasket (4.2L Ford E150, E250, F150)

One of the most important and effective ways to test for a head gasket problem is a chemical block test.

This is due to the fact that in some occasions the engine has a blown head gasket issue, or a cracked block issue, or a cracked cylinder head issue, but the previous 3 tests don't catch it. The only way to be sure it's a head gasket problem or not is doing a chemical block test.

The combustion leak tester (or block tester) test is so effective that it's used in all major/competent repair shops to confirm a blown head gasket issue. In a nutshell this is how the test 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), 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.

Where can you get the chemical and block tester? Here:

Frequently Asked Questions

1.)  How can I tell if the cylinder head is cracked?

The only way to know is to remove the cylinder head and visually inspect it. If the crack is wide enough, you'll be able to easily see it.

In many instances, a visual inspection won't be enough, you'll need to have the machine shop, that's gonna' resurface the cylinder head, for a pressure test.

2.)  Do I need to resurface the cylinder head?

The answer is YES! You should never reinstall the cylinder head or cylinder heads without first having a Machine Shop resurface the cylinders heads (particularly over an overheating condition).

Now, of course, if you (or the machine) have checked it with a straight-edge and there's no warpage, then, and only then is the cylinder head not resurfaced.

3.)  Do I need to remove both cylinder heads from my Ford V6?

Yes, you need to remove them both. In a professional setting, it's standard practice to remove them both and replace both cylinder head gaskets (and have both cylinder heads resurfaced).

This is important because the only way to make sure the other cylinder head isn't extremely warped or cracked is by removing it and and visually inspecting it and taking the necessary warp measurements with a straight edge and doing a pressure test.

More 4.2L Ford Diagnostic Tutorials

You can find a complete list of 4.2L Ford tutorials in this index:

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

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Ford Vehicles:

  • E150 4.2L
    • 1997, 1998, 1999, 2000, 2001, 2002, 2003
  • E250 4.2L
    • 1997, 1999, 2000, 2001, 2002, 2003
  • F150 4.2L
    • 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006