Its a "dreaded" merc 3.7L circa 1986 
Decided to do a comp test while I was doing some mid-summer maintenance (oil change and fuel filters) and was surprised with what I found: #1 -150 #2 - 148 #3 - 152 #4 - 125.
Last comp test I did was 4 yrs ago and was pretty much 153-155 across the board. Totally surprised at the low comp reading in #4. I have absolutely no running issues at all. Idles/runs fine, operating temp right where it should be, no water in oil, no loss of coolant (closed cooling with a 4 inch heat exchanger).
Ran her on the hose for 20 minutes before doing the comp test and batteries were fully charged, all plugs removed and throttle cracked wide open. Ran out there again today, warmed her up, and did the test again (hoping I missed something) same results w/ #4 @ 125. Wet tested #4 and had no change whatsoever in psi.
Dont know what to make of it? I figure if the compression is really that much lower in #4 I would notice something/anything in the way she runs???
Any thoughts?? Thanks guys.
Decided to do a comp test while I was doing some mid-summer maintenance (oil change and fuel filters) and was surprised with what I found: #1 -150 #2 - 148 #3 - 152 #4 - 125.Last comp test I did was 4 yrs ago and was pretty much 153-155 across the board. Totally surprised at the low comp reading in #4. I have absolutely no running issues at all. Idles/runs fine, operating temp right where it should be, no water in oil, no loss of coolant (closed cooling with a 4 inch heat exchanger).
Ran her on the hose for 20 minutes before doing the comp test and batteries were fully charged, all plugs removed and throttle cracked wide open. Ran out there again today, warmed her up, and did the test again (hoping I missed something) same results w/ #4 @ 125. Wet tested #4 and had no change whatsoever in psi.
Dont know what to make of it? I figure if the compression is really that much lower in #4 I would notice something/anything in the way she runs???
Any thoughts?? Thanks guys.
