TEST 2: Are Engine Compression -Exhaust Gases Coming Out Of The Radiator?
The second most common test, to see if the head gasket on your 4.3L, 5.0L, 5.7L GM van (or mini-van, pick up, SUV) is blown or not, is to check if engine compression and/or combustion gases are escaping thru' the cooling system. This is another very easy test and does not require any tools whatsoever to do.
Now, before you start, if the engine has been running for an extended amount of time and it's hot, let the engine cool down for at least 1 hour. This is important, or you run the risk of getting scalded with hot coolant.
If your 4.3L, 5.0L, 5.7L GM van (or mini-van, pick up, SUV) doesn't start, well this is not an issue. OK, here are the test steps:
- 1
Remove your pick up or car's radiator's cap.
- 2
Check the coolant level.
If empty, add some water or coolant to bring the coolant level to full. - 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 radiator will shoot up and out of the now open radiator.
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 radiator.
OK, now that the testing part is done, let's take a look at what your results mean:
CASE 1: The coolant bubbled out or shot out from the radiator. This is bad news and this let's you know beyond a shadow of a doubt that the head gasket on your 4.3L, 5.0L, 5.7L GM van (or mini-van, pick up, SUV) is blown. No further testing is required.
CASE 2: The coolant DID NOT bubble out NOR shoot out from the radiator. So far so good.
If the engine doesn't start or starts but runs with a misfire (rough idle), go to: TEST 3: Checking For a Blown Head Gasket With An Engine Compression Test.
If the engine starts and overheats within minutes, go to: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).
Now, common sense tells you that if a head gasket is blown, you ARE gonna' have oil mixed with coolant, and engine compression and/or combustion gases are going to be shooting out of the radiator but sometimes this just doesn't happen. So, the next test will further confirm or exonerate the head gasket.
TEST 3: Checking For A Blown Head Gasket With An Engine Compression Test
One of the most overlooked tests, to see if the head gasket is bad or not, is an engine compression test. Why? Well because most folks will do the two previous tests (TEST 1 and TEST 2) and they will not see the engine oil mixing with the coolant nor see the combustion gases jumping out of the open radiator and conclude everything is OK. And whatever information they have available never mentions testing the engine compression.
Well, now you know that it is possible for the head gasket to burn and not cause the oil to mix with coolant nor cause the exhaust gases to escape thru' the cooling system. In this test step, you'll be doing a compression test and more importantly, you'll be able to easily interpret those results (with my help) to further confirm or exonerate a blown head gasket.
This test will see if the head gasket on your 4.3L, 5.0L, 5.7L GM van (or mini-van, pick up, SUV) has burned at a point between cylinders.
If this does happen, the compression/combustion of one cylinder to leak into the other and vice-versa and the compression readings will easily let us know this has happened.
OK, here's what you need to do:
- 1
Disable the ignition system.
It's important that spark is not created and delivered to the spark plug wires.
You can easily accomplish this 'disabling' by disconnecting the ignition module's electrical connector or the ignition coil's electrical connector. - 2
Disable the fuel system.
It's important that fuel not be injected into the engine.
You can do this by disconnecting the fuel injectors (if throttle body fuel injection) or the fuel injectors 'Spider' assembly's electrical connector. - 3
Disconnect all spark plug wires (from their spark plugs).
- 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.
NOTE: 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 while you observe the compression tester.
- 7
At the point the gauge's needle stops climbing, have your assistant stop cranking the engine.
- 8
Now, write down the reading and what cylinder it belongs to (you can use the illustration above to help you identify the cylinder) on a piece of paper.
- 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. These compression gauge readings confirm that the head gasket is OK and not burned at a point between two cylinders.
OK, so far all of you resting has confirmed that the head gasket on your 4.3L, 5.0L, 5.7L GM van (or mini-van, pick up, SUV) is not blown, but if your vehicle is still overheating for no apparent cause, I suggest taking a look at the next test: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).
CASE 2: Two side by side cylinders had 0 PSI compression. This engine compression reading confirms that the head gasket is burned thru' at the point between those two cylinders. You will need to replace the head gasket.
