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

Block Tester To Check For a Blown Head Gasket

Every now and then, a blown head gasket on your 4.7L Dodge won't show any of the previous symptoms the previous 3 tests are trying to confirm. In a situation like this, the only way to make absolutely sure the head gasket is blown is by doing a chemical block test.

The combustion leak tester (or block tester) test is used in all major/competent repair shops to confirm a blown head gasket issue. In a nutshell this is how the test 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? You can buy it here:

Frequently Asked Questions

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

The cylinder head has to be removed and visually inspected. If the crack is wide enough, you'll be able to easily see it.

Sometimes, a visual inspection proves inconclusive, this is why it's important to let a machine shop pressure test it for you.

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

YES, you need to resurface the cylinder head! 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.)  Should I remove both cylinder heads?

YES, you should remove them both to visually inspect them both and/or have a machine shop test them for warpage and cracks.

More 4.7L Dodge Tutorials

You can find a complete list of tutorials in this index: Dodge 4.7L Index of Articles.

Here's a small sample of the 4.7L Dodge tutorials you'll find in the index:

  1. How To Test The Fuel Injectors (Dodge, Jeep 4.7L V8).
  2. How To Check Engine Compression (Dodge, Jeep 4.7L V8).
  3. How To Test The COP Ignition Coils (Chrysler, Dodge, Jeep 4.7L).
  4. How To Test The Fuel Pump (4.7L Dodge Dakota, Durango) (at: easyautodiagnostics.com).
  5. How To Test The MAP Sensor (2002-2009 4.7L Dodge) (at: easyautodiagnostics.com).