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 a block test is the only way to confirm (or disconfirm) the problem.

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 Ford 4.6L, 5.4L specific ‘how to’ tutorials that I've written for your troubleshooting and diagnostic benefit. You can find them here: Ford 4.6L, 5.4L Index Of Articles.

Below is a small sample of articles you'll find in the Ford 4.6L, 5.4L index:

  1. How To Test The Thermostat (Ford 4.6L, 5.4L)
  2. How To Test The Engine Coolant Temperature Sensor (DTC P0117, P0118)
  3. How To Diagnose Misfire Codes P0300-P0308 (Ford 4.6L, 5.4L)
  4. Coil-On-Plug (COP) Ignition Coil -Misfire Tests (Ford 4.6L, 5.4L)
  5. How To Test The Crankshaft Position Sensor (Ford 4.6L, 5.4L)
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Ford Vehicles:

  • Crown Victoria
    • 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
  • E150, E250, E350
    • 1997, 1998, 1999, 2000, 2001, 2002
  • Expedition
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Ford Vehicles:

  • Explorer (4.6L)
    • 2002, 2003, 2004, 2005
  • F150, F250
    • 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
  • Mustang (GT & Cobra)
    • 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005

Ford Vehicles:

  • Thunderbird
    • 1994, 1995, 1996, 1997

Lincoln Vehicles:

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    • 2003, 2004, 2005
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    • 1993, 1994, 1995, 1996, 1997, 1998

Lincoln Vehicles:

  • Navigator
    • 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
  • Town Car
    • 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005

Mercury Vehicles:

  • Cougar
    • 1994, 1995, 1996, 1997
  • Grand Marquis
    • 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
  • Mountaineer (4.6L)
    • 2002, 2003, 2004, 2005