How To Test For A Blown Head Gasket (1993-2001 4.0L Jeep Cherokee)

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

Some head gasket failures do not cause the engine oil to mix with the engine coolant or any of the other symptoms you were trying to confirm in the previous 3 tests.

And yet the engine is overheating within minutes of it starting -for no apparent reason.

In these cases a 'block' test is required to pinpoint the problem to the head gasket.

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

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

More 4.0L Jeep Cherokee Tutorials

You can find a complete list of diagnostic tutorials and wiring diagrams for the 4.0L Jeep Cherokee here:

• Jeep 4.0L Index of Articles

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

• Ignition System Wiring Diagram (1993-1995 4.0L Jeep Cherokee)
• How To Test The Crankshaft Position Sensor Jeep 4.0L (1997-1998 4.0L Jeep Cherokee)
• How To Test The Front O2 Sensor Heater (1996 4.0L Jeep Cherokee)
• How To Do An Engine Compression Test (1993-2001 4.0L Jeep Cherokee)