Acceptable compression on '87 4.3?

[Zoomer]

I'm looking at purchasing a boat with a 1987 Mercruiser 4.3 liter 175 HP in it. The dealer said the compression tested cold at 105-110. We tested it warm and it ranged from 125 and 135. I'm new to I/O's, and was wondering if this is acceptable compression? I'm trying to make sure I'm not purchasing a boat with a tired engine in need of replacement soon.<br /><br />Thanks, Zoomer

 

[outboardguy]

Re: Acceptable compression on '87 4.3?

You're fine,when it was new it might have had a bit more.The important thing is that they are equal within 15PSI.If they were below 90PSI then I would worry.

 

[airman]

Re: Acceptable compression on '87 4.3?

Take it for a sea trial. That's your very best test.

 

[Zoomer]

Re: Acceptable compression on '87 4.3?

I'd love to take it out for a trial run, but all our lakes have about 3 feet of ice on them right now. We are planning on using it when fishing season opens the middle of May, and sometimes the lakes don't ice out until about that time. We like the layout and condition of this boat, and would like to get something soon so we can have it ready by May. Running the motor with a water jacket / hose attached, it seems to run pretty good, but I'm certainly no expert when it comes to I/O's. The outdrive sounded quiet and felt smooth, even turning it to the extremes of steering. The bellows didn't feel brittle and looked pretty good. The intial compression numbers seemed so low to me though. For some reason I was expecting something more like 140-160 psi. The warm numbers were a little better, but I wanted to ask an independant party what an acceptable range is for an engine in good condition with some life left in it. I appreciate your replies, and if 125-135 is within the range for this motor in good condition, then that's good news.