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

Block Tester To Check For A Blown Head Gasket

In some cases, the previous 3 tests don't confirm or disprove that the head gasket is good or bad. The only way to find out if the head gasket has failed is by doing a block test.

The block test will tell you without a shadow of doubt if the head gasket is 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 issue 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:

Related Test Articles

There are several more ‘how to’ tutorials that I've written that are 2.4L/2.5L specific, that may be of further help. You can find the ones that are located here, at this site, by going to the 2.4L, 2.5L Nissan Index Of Articles.

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

  1. How To Test The Starter Motor (Nissan 2.4L -Frontier, Xterra).
  2. How To Test Engine Compression (Nissan 2.4L).
  3. How To Test The Fuel Injectors (2.5L Nissan Altima, Sentra) (at: easyautodiagnostics.com).
  4. How To Test The Throttle Position Sensor (1996-1997 2.4L Altima) (at: easyautodiagnostics.com).
  5. How To Test The Power Transistor 2.4L Nissan Frontier, Xterra (1998-2004) (at: easyautodiagnostics.com).
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Nissan Vehicles:

  • 240SX 2.4L
    • 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998
  • Altima 2.4L, 2.5L
    • 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
  • D21 Pick Up 2.4L
    • 1990, 1991, 1992, 1993, 1994

Nissan Vehicles:

  • Frontier 2.4L
    • 1998, 1999, 2000, 2001, 2002, 2003, 2004
  • Pick Up 2.4L
    • 1995, 1996, 1997
  • Sentra 2.5L
    • 2002, 2003, 2004, 2005, 2006
  • Xterra 2.4L
    • 2000, 2001, 2002, 2003, 2004