Blown Head Gasket Test (GM 4.8L, 5.3L, 6.0L)

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

There are times when the engine has a blown head gasket issue, or a cracked block issue, or a cracked cylinder head issue, but the previous 3 tests don't catch it. Is there something else that can be done? The answer is yes! It involves doing a chemical block test.

The combustion leak tester (or block tester) test is used in all major/competent repair shops to confirm a blown head gasket issue. In a nutshell this is how the test 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? You can buy here:

Frequently Asked Questions

1.)  How can I tell if the cylinder head is cracked?

To find out if the cylinder head or heads are cracked, they'll need to be off of the engine block and visually inspected and/or pressure tested.

The pressure test is done by an engine rebuilding machine shop.

If the crack is wide enough, you'll be able to easily see it. If not, the machine shop that'll resurface the cylinder head must pressure test them to find the cracks (if any).

2.)  How can I find out if the cylinder head is warped?

The cylinder head has to be removed from the engine to find out.

Once out, the head gasket surface of the cylinder head has to be perfectly clean. A precision straight-edge tool (along with feeler gauges) is then used to accurately measure the warpage.

Now, if your vehicle overheated and the head gasket is blown, you can bet that the cylinder head is warped and will need to be resurfaced by a machine shop.

3.)  Do I need to resurface the cylinder head?

The answer is YES! You should never reinstall the cylinder heads without first having a machine shop pressure test and resurface the cylinders heads (particularly over an overheating condition).

4.)  Do I need to remove both cylinder heads?

It's standard practice to remove them both and replace both cylinder head gaskets (and have both cylinder heads pressure tested and resurfaced).

This is important because the only way to make sure the other cylinder head isn't extremely warped or cracked is by removing it and and visually inspecting it, warp testing it with a precision straight-edge, and pressure testing it (at your local engine rebuilding machine shop).

More GM 4.8L, 5.3L, 6.0L Tutorials

You can find a complete list of 4.8L, 5.3L, and 6.0L test articles here: GM 4.8L, 5.3L, 6.0L Index Of Articles.

Here's a list of articles you'll find there:

• How To Test The Crank Sensor (at: troubleshootmyvehicle.com).
• How To Do A Compression Test (GM 4.8L, 5.3L, 6.0L).
• How To Test The MAF Sensor.
• How To Test The COP Coils.
• Electronic Throttle Control Test Basics.