2007 5 L MerCruiser

[Rlind111]

Hi all, I’m in the process of buying a 2007 Rinker 320, but I’m not sure if I like these compression readings from the port engine, what is all your opinion. Thanks so much for your time!
138 160
135 155
155 180
140 151

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[alldodge]

A new SBC should have 150 psi compression. Anything much above 150 is saying the gauge is bad or there is some kind of liquid in the cylinder (water or gas).

A old motor should have no more then 10% between the high and low cylinder. Your high is 180 so -18 = 162. Your low is 138 so its way off, your numbers are to far apart.

To do a compression test, the motor should be warm, all plugs removed, ignition coil disabled and throttle at WOT.

Suggest do it again with another gauge, or if it was done correctly I would walk away from the motor because it needs help

Think the boat at 12K dry weight needs 5.7's

 

[Rlind111]

Thanks for your insight, a professional surveyor is the one that did it with four separate gauges. The engine was warm

 

[NHGuy]

So if you like the boat factor in an engine. Boats do eat engines. It causes people to sell them.

 

[QBhoy]

Outside the favourite and usual answer of the gauge being not accurate at all (most aren’t), the only other reason for silly numbers like that would be the engine under suspicion being left too long and having cooled down before the test was done.
As a side note...I also find it ridiculous and entirely in professional for a marine surveyor to have so little faith in his tooling that he has the need to carry 4 compression testers. A professional should use only a calibrated tester. I’m gob smacked

 

[hnt]

So did the surveyor get the same readings for each cylinder using 4 separate gauges? If so, the chances are the engine has issues. What about the readings on the other engine using those gauges? Any sign of water in the oil or steam coming from the exhaust. How do the plugs look? Does the engine turn the proper WOT rpm compared to the other side?