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

Block Tester To Check For A Blown Head Gasket

Using a block tester, to check for a blown head gasket when the previous 3 tests don't confirm it, will tell you without a shadow of doubt if it's blown or not.

Why didn't I start of with this test? Because TEST 1, TEST 2, and TEST 3 usually pinpoint 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:

  • 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), combustion gases are entering the radiator. This result confirms a head gasket failure, a cracked blocked, or a cracked cylinder head issue.
  • If the blue chemical doesn't change color, you can conclude that you don't have a head gasket failure, a cracked blocked, or a cracked cylinder head issue.

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

More Ford 4.0L Ford Explorer And Aerostar Tutorials

There are several more 4.0L Ford Explorer (Aerostar, Mountaineer) 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:

Here's a sample of the test articles you'll find in the index:

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Ford Vehicles:

  • Aerostar 4.0L
    • 1991, 1992, 1993, 1994, 1995, 1996, 1997
  • Explorer 4.0L
    • 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010

Mercury Vehicles:

  • Mountaineer 4.0L
    • 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010