Low Compression Optimax

[Tbasser]

03 Optimax 225hp, stock, low hrs, around 120. Have a base gasket leak, powerhead to adalptor. Took it in for warranty repair, warranty runs out in 2 weeks. Prior to taking it in I performed a compression test. Cold engine, 30 degree temp outside, sitting for the winter. All the reading were close 91 to 95 lbs. I know to get good readings a warm engine is required. I explained my readings to the Mercury mechanic and he didn't think they were bad. Any comments would be appreciated. Thanks, Terry

[150aintenuff]

if its cold chances are its not sealing due to shrunk pistons, rings, and cyl walls... aluminum shrinks more than the bores so its likely that the pistons shrank enough that the ring gaps are widened enough due to cold temps to blead by... also cold temps equal low voltage and slow cranking allowing for more blead by.. retest hot after you get it back and see what the true number are before you get to worried but if its 90PSI hot id want to look closer at it.... especially if there is a large spread across the cyl...

[Eagle One]

Hard to check when the engine is that cold. Need to warm it up on a hose and check it. 120 is about normal on a warm engine. I'd think the rings were sorta stuck with the temp that low. any oil on them is likely to be like honey.

[Tbasser]

Thanks for the replies. Due to a planned trip I won't be able to check the compression when hot prior to warranty running out. I'll call the Merc mechanic and see if he will do it when his repairs are done. I'll have to beg because he thinks all is good. Thanks, T

[flabum1017]

have him do it before he starts the repairs.... so if he finds them too low, he will have to pull the powerhead only once

[150aintenuff]

if I recall there is a minimum reccomended compression on those motors around 90 PSI warm in the service manuals.... id have him check justin case.....

[oldmercman]

Do a leak down test on it. More then 20% leakage you may have a problem. Carbon has been a big problem in that motor. Make sure that it is coming up to temperature at least 125 degree on each head. The thermostat may be leaking by. The air injectors can leak air back into the rails. Run a 6 gallon tank of gas with a bottle of Yamaha Ring Free in it, run the motor hard at the lake, also run a 1/2 can of Power Tune thru the air compressor intake at idle, that will clean the air injectors. Run the boat full speed to clean it all out then do compression test with the motor warm. Run Yamaha Ring Free with your gas at all times.