TEST 4: Engine Compression Test
In extremely rare cases, one of the 2 head gaskets gets burned in the spot right between two adjacent cylinders. This results in the compression of one cylinder to escape into the other and vice-versa.
The end result of this condition that the engine runs, but runs with a misfire. The way to check this by doing a compression test. Now, doing a compression test on the Ford Escape's 3.0L engine is not for the faint of heart, since the upper manifold plenum has to be removed. So, if one of the previous 3 tests have confirmed a blown head gasket, you can skip this test.
These are the test steps:
Remove the ignition coils. This will require that you remove the upper intake manifold plenum and may have to consult a repair manual for the specifics of this procedure.
Remove the spark plugs and install the compression tester (hand tight only) on the first cylinder you're gonna' test.
Have a helper crank the engine while you observe the compression tester. When the needle stops moving, have your helper stop cranking the engine.
Write down the compression readings. Repeat on the next 5 cylinders.
Let's take a look at what your test results mean:
CASE 1: You got 2 side by side (adjacent) cylinders with 0 PSI. This confirms beyond a shadow of a doubt that you do have a blown head gasket on your hands.
CASE 2: All cylinders had sufficient compression. This is the correct and expected test result and tells you that both head gaskets are not blown between any 2 adjacent cylinders.
Frequently Asked Questions
1.) How can I tell if the cylinder head is cracked?
The cylinder head has to be removed and visually inspected. If the crack is wide enough, you'll be able to easily see it.
Sometimes, a visual inspection proves inconclusive, this is why it's important to let a machine shop pressure test it for you.
2.) Do I need to resurface the cylinder head?
YES, you need to resurface the cylinder head! You should never reinstall the cylinder head or cylinder heads without first having a Machine Shop resurface the cylinders heads (particularly over an overheating condition).
Now, of course, if you (or the machine) have checked it with a straight-edge and there's no warpage, then and only then is the cylinder head not resurfaced.
3.) Do I need to replace both cylinder head gaskets?
YES, you need remove both cylinders heads and replace both gaskets. You'll need to have both cylinders heads checked for cracks and resurfaced.