compression check results

[D.L.Russell]

I'm checking out a boat for purchase. It has a 5.0L Mercruiser. 1995 engine. The compression read, cyl 1 145, cyl 2 145, cyl 3 145, cyl 4 145, cyl 5 130 , cyl 6 145, cyl 7 135, cyl 8 145.<br /><br />Any opinions?

 

[petryshyn]

Re: compression check results

A compression test can be a very subjective test, pending on your technique. Did the first hit on that cylinder yeild a high presuure? Did each cylinder hit the same number of times? Generally the difference between the highest and lowest cylinder should be within 10-15 psi pending on the overall average. It appears that you are right on the edge of the acceptable limt. This could be the result of an actual engine problem, carbon deposited on the valve when removing plugs or simply technique. I would recommend reinstalling the plugs, run the engine for a few seconds, then retest. If the difference is still apparent, I would procede to do a cylinder leak-down test which will tell you exactly where the leakage is occuring. If you don't have the equipment to do a leak down test, do a wet test on the low cylinder and look for a rise in compression. There is more to a compression test that meets the eye. The first symptom of borderlined UNEVEN compression will be rough idle. . . .good luck

 

[D.L.Russell]

Re: compression check results

Thanks for the advice. The idle is very smooth. An in water test was very positive. I did not have a chance to do a wet test but will.

 

[ozarkjeep]

Re: compression check results

if it runs/starts good Id go with it ( take the risk)<br /><br />assuming of course it has good oil pressure when warm, thats as important to me as good compression.

 

[manowar]

Re: compression check results

Ill bet that you only have a little carbon buildup and maybe a worn head gasket or both