Lost compresslon

2010 Ford Fusion 2.5 220,000 miles.
I don’t need recommendations for this, it’s going to the shop. Just curious about this and was hoping to learn something. 16 months ago my son in law brought me this car he purchased to have me fix anything it might need. It was in good shape except for 1 coil and oil filled spark plug Wells. I changed coil and intake gasket. I did a compression test. 3 cylinders had 180 lbs. But #2 cylinder had 165. He called me today with a misfire. This time I got 180 lbs on 3 cylinders and on cylinder #2 30 lbs dry and 63 lbs wet. There is absolutely no abnormal mechanical sounds from either top or bottom of the engine. My first question is should I have been alarmed when cylinder 2 was a little lower than the rest? My second question is why is only one cylinder affected. My first impression is that somebody changed the plugs way back and didn’t clean the oil out of the wells before removing plugs. But if that’s the case, wouldn’t all cylinders be affected as they were all filling with oil. What else could cause ring or bore damage on just one cylinder?

This car is probably burning oil at an alarming rate.Only a ring job could fix it.

Sounds like a burnt or sticky valve, if the other 3 are at 180.


I’ve fixed a few headgaskets that failed where the breech had no effect other than loss of compression. Could be bad valve, rings or piston as well. Only taking it apart will tell for sure.

Don’t believe oil in plug well idea is contributory.

Yes, initial low reading was cause for concern. If it had been failed head gasket to water jacket, it could have been causing much more destructive damage from bearings being exposed to coolant.

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Your last sentence assumes that all the cylinders would “fill with oil”… Why would the cylinders fill with oil? Having oil in the plug well only indicates that the valve cover was leaking down into the well, not that the cylinder was filling up nor that any oil that did fill it up, made its way into the cyl. Even if it did make it into the cyl…it wouldn’t be enough to do any damage.

You more than likely have a burned or stuck open exhaust valve and not ring or bore damage. I think you are assuming the engine was hydro-locked from the plug well oil… You need a lot more liquid than would be in the well to cause permanent damage to a cylinder, ring or Con Rod.

I’m going with a burned or stuck valve here, you aren’t looking for ring or bore damage but something to do with a valve.

The wells were filled with oil. I don’t know if the previous owner would clear the oil before removing the spark plugs which would put oil in the cylinders. My fear was that contaminated oil could damage the rings or bore. I am getting encouragement from you guys that it may be an upper engine problem though.

Do a leak down compression test on that cylinder. Listen to the various points of egression with a sthescope? i.e. the intake manifold, the exhaust, the crankcase, the head gasket seam, and look for bubbles in the cooling system. Where you find the leak will point you to the culprit.

When you add oil to a cylinder and it raises the compression, it indicates the compression rings are worn in that cylinder.


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Even with the oil, that cylinder is still 120 lbs lower than the rest

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And your point being?



I know that if adding oil causes higher compression it is an indication of ring failure, but I don’t know how much of a difference between wet and dry would determine ring failure. Is 30 lbs difference enough to indicate rings? At any rate, the engine has over 210,000 miles, and I don’t think an upper or lower rebuild would be worth it. The best option I think is to put in a Jasper. But the kids can’t afford that, so we are leaning towards a low milage used engine with 70,000 miles.

The test indicated that there’s something seriously wrong with the rings/cylinder wall of that cylinder. Or the rings are cracked.


Thank you. All I’ve had on that was head knowledge

Thank you guys for the responses. The purpose of this thread was for me to learn a couple of things and that I did. The Fusion is now in a shop that I know nothing about getting a used engine installed. They diagnosed it as a hole in the piston (which I totally disagree with based on wet compression test) or a burnt valve. Either way the engine damage at 220,000 miles warrants replacement. There is not a Jasper available for this, and the kids couldn’t afford that anyways. Again thanks for all your input.

Yes, you did nothing wrong. The only test I’d have added would have been to check the valve clearance at the upper end.

I’m wondering if they’ll find a loose exhaust valve seat. Some of these engines had that problem. Apparently this reduces valve clearance and causes symptoms like you describe.