TEST 2: Exhaust Gases Shooting Out Of The Radiator
IMPORTANT: This test must be done with a completely cold engine!
For our second test, we're going to remove the radiator cap from the radiator and then crank the engine.
What we're looking for is to see if the coolant will remain undisturbed or if it will be shot out.
If coolant shoots out of the radiator when you crank the engine, you can conclude that one or both of the head gaskets are blown.
If the coolant remains undisturbed, then your next step is to go on to the next test.
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!
NOTE: Most of the vehicles covered by this tutorial have a radiator that does not have a radiator cap. You'll need to remove the coolant tank's cap to perform this test (see photo 2 of 2 above).
These are the test steps:
- 1
Remove the cap from the coolant tank (or radiator if the radiator has a radiator cap).
If the coolant tank is not full, then top it off with water. - 2
Have your helper to crank the engine, while you stand at a safe distance from the open coolant tank (or radiator).
- 3
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 examine your test result:
CASE 1: The coolant bubbled out or shot out from the coolant tank (radiator) as the engine was cranked. This result confirms that one or both of the head gaskets are 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, in your 3.4L V6 Chevrolet (Pontiac), go to: TEST 3: Cylinder Compression Test.
If the engine, in your 3.4L V6 Chevrolet (Pontiac), runs but overheats, go to: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).
TEST 3: Cylinder Compression Test
If you take a moment and look at the photo at the beginning of this tutorial, you'll notice that the head gasket has burned at a point between two side-by-side cylinders.
Although this type of failure is not common, it does happen. And when it does happen, those two side-by-side cylinders will not produce any compression.
The end result is that the engine either does not start or starts and runs, but only runs with four cylinders (since those two are dead).
The only way to test this type of head gasket failure is 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 (3.4L V6 Chevrolet, Pontiac).
These are the test steps:
- 1
Disconnect the ignition control module assembly from its electrical connectors. This is will disable the ignition system and is an important safety precaution.
- 2
Remove the fuel pump relay.
- 3
Disconnect all spark plug wires (from their spark plugs).
NOTE: Before disconnecting them, label them with the number of the cylinder that they belong to. - 4
Remove all of the spark plugs.
- 5
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. - 6
Have a helper crank the engine as you observe the compression tester.
- 7
When the gauge's needle stops climbing, have your assistant stop cranking the engine.
- 8
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).
- 9
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 gaskets are 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 both head gaskets.
