Low compression 0/B

[jwclbi]

Hello, Recently compression tested my 1998 225EFI Merc and discovered after 800 hours the compression is down to low to mid 90's on all cylinders. The engine still runs fine but was talking to a couple guys who suggested putting new rings in it. Anyone have any information on this and if it works? I know its big job and was thinking if its worth doing on an older engine. Thanks

[flyingfrizzle]

Originally Posted by jwclbi

Hello, Recently compression tested my 1998 225EFI Merc and discovered after 800 hours the compression is down to low to mid 90's on all cylinders. The engine still runs fine but was talking to a couple guys who suggested putting new rings in it. Anyone have any information on this and if it works? I know its big job and was thinking if its worth doing on an older engine. Thanks

The 3.0 mercurys run lower compression than the 2.5's. The 2.5's should have 120-130ish psi where the efi 3.0 litter efi motors spec only 90-110psi so your right where you should be for 800 hrs. I had a 225 with mid 90's across the board and it done fine with plenty of power. The main thing you want to be concerned with is any diffrences between the readings. You want them to be with in 10% and with in 5% is really good for 800 hrs. Also do a leak down test. That will tell you the real deal. You want low leak down numbers. This will tell you a lot better condition of the rings and calendar condition. IF they are ALL in the mid 90's and you get fair leak down numbers I say run the crap out of it till you see one starting to drop off, THEN worry. Only problem is when the rings wear down and loose their bevel the edges can flatten out and it will snag a port easier. I you decide to do it, it is a major job for someone with little experience but not bad to do if you have a little experience plus the tools and time to do. Follow the factory manual. It will help tons. To me It would be worth rebuilding and saving if it don't need to be re-bored and had bad scratches in the cyls. Cost to do that will make it a parts motor.

[Bigshrimpin]

Those 3.0L 1995 - 1998 225EFI's had notches in the exhaust ports which lower the compression to improve idle and starting. If they are all even at 95psi I wouldn't be concerned.

This is a picture of a 2.5L 150 that also has a similar notch.

[flyingfrizzle]

Originally Posted by Lordwrench

Friz, a bud of mine is doing compression checks on some opti's tonight, obviously they are EFI but can u confirm that chart is referenced for opti's too?Also, I would like a spec chart for my 175 pro XS...


B

I tried to post the factory service manual but it is just way to big to post, I maybe can send it to you email tho.