Compression 1990 Merc 260

[James B]

I took our boat in for annual service. Mechanic preformed compression check. Poor compression was discovered. 85 psi in two, 100 psi in two, and 135 psi in four. Repair estimate is $3,750.00. <br /><br />I believe problem is due to motor overheating last spring. New impeller was installed, solved cooling problem. <br /><br />Motor ran fine all summer even with weak compression. Mechanic is telling me problem will only get worse. Would not address how fast problem will progress, only that the weak cylinders will eventually fail. <br /><br />If I cheap out, what are the odds of the motor lasting through the season?<br /><br />Thanks, <br /><br />James

 

[trog100]

Re: Compression 1990 Merc 260

i think it will keep going like that for ages.. poor compression caused by overheating is cos the pistons expand too much.. get tight in the bores and the aluminum scuffs causing the rings to seize in their groves.. hence the poor compression..<br /><br />if it ran all last summer like that i dont see any reason it shouldnt do the same this summer..<br /><br />dont thrash the arse of the poor thing and keep an eye on the oil level cos it is likely to be burning some..<br /><br />not the normal answer u will get on here and i am sure to get flamed for not saying fix it now.. but that is my opinion.. <br /><br />trog100

 

[Haut Medoc]

Re: Compression 1990 Merc 260

If it is raw water cooled, run it till it croaks. If it is fwc, run it till it don't run so good, and rebuild it.You didn't say what engine you have but I bet you could get a rebuilt block alot cheaper than 3,750. Keep an eye on the oil, she'll probably burn some now.

 

[James B]

Re: Compression 1990 Merc 260

Trog and J.Kopec, <br /><br />Thank you.<br /><br />The motor is a 5.7 Mercruiser. I do not know the difference between raw water cooled and FWC. It sucks water out of the lake. I would guess that makes it a raw water cooled.

 

[xltier]

Re: Compression 1990 Merc 260

there are engine rebuilders around here and they ask if its marine or not.if yes than its only 100.00 more than a truck engine.$3750.00!!wow.i wish we could get that much.

 

[weatherz]

Re: Compression 1990 Merc 260

Wonderin why it's 100.00 more for a marine engine? I cant think of anything that would be different as far as a short block internals?

 

[waterone1@aol.com]

Re: Compression 1990 Merc 260

Just off the top of my head....the freeze plugs, the head gaskets, etc.

 

[QC]

Re: Compression 1990 Merc 260

I would run it too. Compression checks aren't very accurate anyway. I would do a balance test at idle just to make me feel better. Pull off one plug wire at a time and then replace it; doing all 8. It should run equally rough and sound very similar with each dead hole. If there is one that makes LESS of an impact on the sound etc. then that hole would be the one I was concerned about. Could be a bad plug that causes that too though, so don't jump off the dock before checking out the weak sister if there is one. If they seem relatively "balanced" then there is probably nothing wrong.<br /><br />Like the others I would watch the oil and am very curious how much it burned last season. If it has stayed the same then there was probably nothing wrong in the first place.