TEST 2: Wet Compression Test
If your test results (from TEST 1) indicate one or several cylinders with low compression, the next step is finding out what is causing it.
What's usually causes a cylinder to have low compression is one of two conditions: either its piston compression rings are severely worn or the its intake or exhaust valve are severely worn.
Thankfully, you and I can find out by ... your next step is repeat compression test after adding a little oil to the affected cylinder. This is known as a ‘wet’ compression test.
If the low cylinder compression is due to worn rings, the compression value of the affected cylinder will go up. If the problem is caused by worn cylinder head valves, the compression value will stay the same.
These are the test steps:
Add a tablespoon (or two) of engine oil in the cylinder you need to retest. I suggest using a small and long funnel so that the oil will reach the inside of the cylinder.
Once you've added the oil, install the compression gauge, and as before... just hand tighten it.
Now, have your helper crank the engine till the needle stops climbing on the compression gauge.
As before, your job is to keep an eye on the gauge, and you'll see one of two results:
1.) The needle will climb higher than the previous compression number you recorded for this specific cylinder, or...
2.) The needle will not move at all or stay at the same number you recorded earlier.
What ever value your compression tester reads, write it down again.
If you have another cylinder that needs to be tested... repeat steps 1 thru' 4 on it now.
Let's take a look at what test results mean:
CASE 1: The compression value went up after adding motor oil and retesting. This tells you that the low compression problem is due to worn piston compression rings.
Here's why: The motor oil you just added helped the piston rings to create a tighter seal. With the piston rings now sealing the compression inside the cylinder, the compression value on your compression tester went up. This type of test result only happens when the problem is due to worn piston rings.
CASE 2: The compression value DID NOT go up after adding oil and retesting (in other words, it stayed the same). This result tells you that the low compression value registered in this cylinder (in the dry test) is due to worn/damaged cylinder head valves.
The Intake Manifold Plenum Has To Be Removed
The thing that complicates doing a compression test on your 3.0L Ford Escape (3.0L Mazda Tribute) is the fact that the upper intake manifold plenum must be removed to access cylinders 1, 2, and 3 of bank 1.
I don't include any instructions on this procedure, so you may want to buy a repair manual for this procedure.
For the DIY'er that doesn't have a lot of wrenching experience, this might be a job that's best left to an experienced automotive mechanic/technician. Since paying for his expertise may end up saving you from a tremendous headache.
If you do tackle the compression test job, here are some pointers:
- As you're removing bolts, nuts, etc... place them in a container and away from the engine. This is important since you'll want to avoid having anything fall into the open intake manifold runners (that will be exposed when the plenum is removed).
- You WILL NOT be able to place rags in the open intake runners while doing the compression test. Why? Because if you do place rags in the open intake runners (to avoid stuff falling into them)... these rags will get sucked into the cylinder as the engine cranks.
- Use new gaskets. Do not re-use the old intake manifold plenum gasket. Also, when installing the new one, do not coat it in any type of sealer (like RTV Silicon). This is not necessary and could back fire on you since the sealer can cause a vacuum leak.
Yes, testing engine compression on the 3.0L Ford Escape (3.0L Mazda Tribute) isn't for the ‘faint of heart’. So take all necessary safety precautions and avoid having anything fall into the open intake manifold runners. Or consider letting a professional mechanic do it.
Which Compression Tester Should I Buy?
There are lot of engine compression testers to choose from and many places to buy them. I'm gonna' make two recommendations to you:
1) Which one to buy: The engine compression tester that I have always used is the Actron CP7827 Compression Tester Kit. My only complaint about this engine compression tester is that it does not come with a case to store it in.
Engine Compression Gauge Testers
2) Where to buy: You can buy an engine compression tester just about anywhere, but you'll end up paying more for it (especially at your local auto parts store). The above links will help you comparison shop. I think you'll agree it's the better way to save money on the compression tester!