TEST 2: Compression Gases Escaping From An Open Radiator
The second most common test, to see if the head gasket on your 3.8L GM car or mini-van 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.
IMPORTANT: 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 3.8L GM car or mini-van doesn't start, well this is not an issue. OK, here are the test steps:
- 1
Remove the cap from the radiator.
- 2
Check the coolant level since the radiator has to be full of coolant for this test to work.
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 3.8L GM car or mini-van is blown. No further testing is required.
CASE 2: The coolant DID NOT bubble out NOR shoot out from the radiator. This is the correct and expected test result.
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. Go to: TEST 3: Checking Engine Compression.
TEST 3: Checking Engine Compression
In some particular cases, the head gasket burns in a spot right between to side-by-side cylinders.
When this happens, and if the engine starts, the engine will run with two dead cylinders.
The image, of the blown head gasket, I'm using at the beginning of this tutorial shows this exact type of head gasket failure.
If this does happen, the compression/combustion of one cylinder will leak into the other and vice-versa. This will cause both side-by-side cylinder to have 0 PSI compression.
We'll perform an engine compression test to find out if this has happened.
OK, here's what you need to do:
- 1
Disable the fuel system and the ignition system. It's important that fuel not be injected into the engine and spark not be delivered to the spark plug wires.
You can do this by disconnecting ignition control module's electrical connector (this will disable both systems). - 2
Disconnect all spark plug wires (from their spark plugs) and then take out all of the spark plugs.
NOTE: Label all of the spark plug wires before you unplug them from the spark plugs, that way you'll know where they go when you're done. - 3
Install the compression tester 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 while observing the compression tester.
- 5
When the compression tester'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 image 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. These compression gauge readings confirm that the head gasket is OK and not burned at a point between two cylinders.
If you still suspect that the head gasket on your 3.8L GM car or mini-van is blown, take a look at: 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.
