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

How To Test For A Blown Head Gasket (4.2L Ford E150, E250, F150)

Sometimes, a blown head gasket can be very hard to diagnose and pin-point as the cause of the problem and 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:

  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 engine is started.
  4. 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.
  5. 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.
  6. 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? Here:

Is The Cylinder Head Cracked?

You might be wondering how can you find out if the cylinder head is cracked or not. The only way to tell is to remove it and visually check for them on the surface that faces the engine block's deck.

If no cracks are visible to the naked eye, then the next very important step is to have it pressure tested (or whatever other method) by your engine machine shop.

More Ford 4.9L, 5.0L, 5.8L Tutorials

There are several more 4.9L, 5.0L, 5.8L Ford specific ‘how to’ tutorials that I've written for your troubleshooting and diagnostic benefit. To go there now, click here: Ford 4.9L, 5.0L, 5.8L Index Of Articles.

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

  1. Manifold Absolute Pressure MAP Sensor Test (Ford 4.9L, 5.0L, 5.8L).
  2. Ignition Coil Test -No Spark No Start Tests (Ford 4.9L, 5.0L, 5.8L).
  3. How To Troubleshoot A No Start (Ford 4.9L, 5.0L, 5.8L).
  4. Testing A Blown Head Gasket (Ford 4.9L, 5.0L, 5.8L).
  5. How To Test Engine Compression (4.9L, 5.0L, 5.8L).
  6. How To Test The Ford Mass Air Flow (MAF) Sensor (at: easyautodiagnostics.com).
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Ford Vehicles:

  • Bronco 4.9L, 5.0L, 5.8L
    • 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996
  • Crown Victoria 5.0L
    • 1989, 1990, 1991
  • E150, E250, E350 4.9L, 5.0L, 5.8L
    • 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996

Ford Vehicles:

  • F150, F250, F350 4.9L, 5.0L, 5.8L
    • 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997
  • Mustang 5.0L
    • 1988, 1989, 1990, 1991, 1992, 1993
  • Thunderbird 5.0L
    • 1988, 1989, 1990

Lincoln Vehicles:

  • Continental
    • 1988, 1989, 1990
  • Mark VII
    • 1988, 1989, 1990, 1991, 1992
  • Town Car
    • 1988, 1989, 1990

Mercury Vehicles:

  • Cougar 5.0L
    • 1988, 1989, 1990

Mercury Vehicles:

  • Grand Marquis 5.0L
    • 1988, 1989, 1990, 1991