TEST 2: Compression Pressure And/Or Exhaust Gas Exiting The Radiator
The next test is as easy as the first one, but... you need to keep in mind that the engine must not be HOT! In this test, you're gonna' check to see if the compression/exhaust gases are flowing into the radiator and exiting out of the radiator's open neck (or open expansion tank if the radiator does not come equipped with a cap).
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 4.6L, 5.4L Ford van (or car, pick up, SUV) 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 (if not equipped with a radiator cap, then remove the expansion tank's cap). Check the coolant level, since the radiator (or expansion tank) 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 (or open expansion tank).
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 shot out from the radiator (or expansion tank): This is bad news and this let's you know beyond a shadow of a doubt that the head gasket on your 4.6L, 5.4L Ford van (or car, pick up, SUV) is blown. No further testing is required.
CASE 2: The coolant DID NOT bubble out NOR shoot out from the radiator (or expansion tank): So far so good, but one more test is needed to make absolutely sure the head gasket is OK, go to: TEST 3: Checking Head Gasket with a Compression Test.
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 Head Gasket With A 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 4.6L, 5.4L Ford van (or car, 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:
Disable the ignition system on your 4.6L, 5.4L Ford van (or car, pick up, SUV). It's important that spark is not created and delivered to the spark plug wires.
If you have the two coil pack setup (4.6L engines), then you need to disconnect both coil packs from their electrical connector.
If your 4.6L, 5.4L has the COP coils, removing them (to remove the spark plugs in step 3), will disable the ignition system.
Disable the fuel system. It's important that fuel not be injected into the engine.
You can do this by disconnecting the fuel injectors or by removing the fuel pump relay.
Remove all of the spark plugs
Be careful and don't drop any on the floor or the spark plug's porcelain insulator can break (and then you'll have a misfire on your hands later).
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.
Let's take a look at your test results:
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, 3 out of 4 tests have confirmed that the head gasket on your Ford 4.6L, 5.4L van (or car, pick up, SUV) is not blown. But but if your Ford is still overheating for no apparent reason, take a look at the block test here: 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.
Let me give you a more specific example: 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 Ford pick up and I got the following compression tester readings:
- Cylinder #1 = 165 PSI
- Cylinder #2 = 180 PSI
- Cylinder #3 = 0 PSI
- Cylinder #4 = 0 PSI
- Cylinder #5 = 170 PSI
- Cylinder #6 = 170 PSI
- Cylinder #7 = 175 PSI
- Cylinder #8 = 175 PSI
The compression readings for cylinders #3 and #4 would be a dead giveaway that the head gasket got fried between those two cylinders. Now, in your Ford van (or car, pick up, SUV), you may not see those exact same cylinders with 0 PSI readings. It may be #1 and #2 or it may be #5 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.