TEST 2: Exhaust Gases Shooting Out Of The Radiator
The second most common test is to remove the radiator cap (from the radiator) and then crank the engine to see if coolant gets shot out of the radiator.
A sure sign of a blown head gasket is seeing coolant shooting out of the radiator while cranking the engine.
If the coolant remains undisturbed, your next test is TEST 3 or TEST 4.
CAUTION: Do not remove the radiator cap from the radiator if the engine is hot. If the engine has been running for any length of time, then let it cool down completely before removing the radiator cap!
These are the test steps:
- 1
Remove the radiator cap.
- 2
Check the coolant level inside the radiator and add if necessary.
- 3
Have your helper to crank the engine, while you stand at a safe distance from the open radiator.
- 4
You'll see one of two results:
1.) The water or coolant inside the coolant tank (or radiator) will shoot up and out.
2.) The coolant will not be disturbed. In other words, cranking the engine will have no effect on the level of the water or coolant in the coolant tank (or radiator).
Let's see what your test result means:
CASE 1: The coolant bubbled out or shot out from the radiator as the engine was cranked. This test result tells you that the head gasket is blown.
CASE 2: The coolant DID NOT bubble out NOR shoot out from the coolant tank (radiator) as the engine was cranked. This is the correct test result.
If the engine doesn't start, go to: TEST 3: Cylinder Compression Test.
If the engine runs but overheats, go to: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).
TEST 3: Cylinder Compression Test
In some cases, the head gasket failure will cause the engine not to start because it has failed in a section between two cylinders.
When this type of head gasket failure happens, the two side-by-side affected cylinders will not produce any compression whatsoever. Therefore, with two dead cylinders, the engine will not start.
You and I can quickly check this type of failure by doing an engine compression test.
I've written a more detailed engine compression test tutorial which you can find here: How To Test Engine Compression (2004-2006 2.8L Chevrolet Colorado, GMC Canyon).
These are the test steps:
- 1
Disconnect and remove the ignition coils.
- 2
Remove all of the spark plugs.
- 3
Thread in the compression tester by hand, on the first spark plug hole you're gonna' start with.
Do not use any tools to tighten the compression tester. Hand tightening the compression tester is more than enough to get the proper results. - 4
Have a helper crank the engine as you observe the compression tester.
- 5
When the gauge's needle stops climbing, have your assistant stop cranking the engine.
- 6
Write down the reading and what cylinder it belongs to on a piece of paper (you can use the illustration above to help you identify the cylinder).
- 7
Remove the compression tester and repeat the above steps in the remaining cylinders.
OK, let's take a look at what your results mean:
CASE 1: All cylinder compression readings where normal. This is the correct test result and it confirms that the head gasket is OK (not burned at a spot between two side-by-side cylinders).
If you still suspect a blown head gasket, go to: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).
CASE 2: Two side by side cylinders had 0 PSI compression. This test result confirms that the head gasket is burned thru' at the point between those two cylinders. You will need to replace the head gasket.
