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.
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 3.8L GM car or mini-van doesn't start, well this is not an issue. OK, here are the test steps:
Remove your pick up or car's radiator's cap. 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.
Now, get your helper to crank the engine, while you stand at a safe distance from the open radiator.
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
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 3.8L GM car or mini-van 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:
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).
Disconnect all spark plug wires (from their spark plugs) and then take out all of the spark plugs. I suggest you 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.
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.
Have a helper crank the engine. Your job is to observe the compression tester.
This is what is gonna' happen: The compression tester's needle will climb, as the engine cranks, till it reaches the maximum cylinder compression. At the point it stops climbing, have your assistant stop cranking the engine.
Now, write down the reading and what cylinder it belongs to (you can use the image in the image viewer to help you identify the cylinder) on a piece of paper. Remove the compression tester and repeat the above steps in the remaining cylinders.
OK, before I jump into the above compression test result interpretations, let me give you some more detailed information as to what you're trying to accomplish with this test, If the head gasket is burned at a location between 2 cylinders, your compression test readings will give you 2 good compression readings and 2 compression readings that will be 0 PSI. Let me give you a more specific example:
Let's say that I tested my 3.8L GM car or mini-van and I got the following compression tester readings:
- Cylinder #1 = 165 PSI
- Cylinder #2 = 180 PSI
- Cylinder #3 = 0 PSI
- Cylinder #4 = 170 PSI
- Cylinder #5 = 0 PSI
- Cylinder #6 = 170 PSI
The compression readings for cylinders #3 and #5 would be a dead giveaway that the head gasket got fried between those two cylinders. Now, in your 3.8L GM car or mini-van, you may not see those exact same cylinders with 0 PSI readings. It may be #1 and #3 or it may be #4 and #6, the key here, is that whatever cylinders are affected, two of them will have 0 PSI compression and they will be both be side by side.
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.