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

Block Tester To Check For A Blown Head Gasket

In the tough to diagnose blown head gasket cases, the previous 3 tests will not confirm or disconfirm a blown head gasket. In these cases, the one test that will settle the matter in a definitive way is a block test with a combustion leak detector.

Why didn't I start of with this test? Because TEST 1, TEST 2, and TEST 3 usually pin-point a blown head gasket condition in about 95% of the cases (not to mention you don't have to spend any $$ to do them). It's the remaining hard to diagnose 5% percent where the effort of finding a block tester is worth it.

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.

You can buy one here:

Related Test Articles

There are several more GM 3.1L, 3.4L specific ‘how to’ tutorials that I've written for your troubleshooting and diagnostic benefit. The articles that are here in this web site, you can find them here: GM 3.1L, 3.4L Index Of Articles.

The following articles are found at easyautodiagnostics.com, which is the other Web Site that I write for.

  1. How To Test The Ignition Coil Packs (GM 3.1L, 3.4L).
  2. Testing The Ignition Module And Crank Sensor (GM 3.1L, 3.4L).
  3. How To Test The MAF Sensor.
  4. How To Clean The MAF Sensor.
  5. How To Test The Throttle Position Sensor (TPS) (GM 3.1L, 3.4L).
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