2003 Mercury 90HP 4-stroke crankcase oil level rises

[fortran]

2003 Mercury 90HP 4-stroke on a Boston Whaler Montauk 170 (17'). 65 hours on the motor; run at 6,225-ft. elevation (Lake Tahoe); 13 3/4" x 15"P prop; 5800 RPM at WOT. <br /><br />Problem: crankcase oil level rises, oil gets thinner, turns a thin black color, and smells a little like gas. For example, oil level on the dipstick rose 15/16ths of an inch after 7 1/2 hours of use -- translates to 4 3/4 quarts in, about 5 1/2 quarts out.<br /><br />Oil has been changed at least six times. According to one of the two dealers that I've taken it to, engine temp is normal; compression is 192, 195, 194, and 187; and cylinder leakage tests show 6%, 6%, 5%, and 10%. Fuel pump is fine (yet replaced twice). Appears to be no water in the oil (oil isn't milky, no water comes out when oil is drained). There's a little carbon around the exhaust port and on the plugs. Don't usually use it but the primer bulb never (15+ pumps) gets hard. Generally, the motor runs fine. Occansionally, after running for one to two hours at varying RPM and then stopping for five to ten minutes and then starting up and running below 2000 RPM, the motor runs roughly. Running it for a few minutes at high RPM causes it to run smoothly again.<br /><br />The dealers don't know why the oil level rises.<br /><br />Thanks for any help,<br />Bill L.

 

[The Marine Doctor]

Re: 2003 Mercury 90HP 4-stroke crankcase oil level rises

It sounds like the engine is running rich. It is normal for fuel to enter the crankcase...but the oil is to be burnt off at much the same rate, this will keep the level at full.<----also the reason it's imparative to change the oil <br /><br />All 4 stroke engines burn oil.<br /><br />In some situations the fuel will enter the crankcase quicker than the oil being burnt off. This is your situation.<br /><br />Get your dealers to find out what is causing the rich condition...this should take care of the problem you are having.<br /><br />TMD

 

[JB]

Re: 2003 Mercury 90HP 4-stroke crankcase oil level rises

Many Yamaha F80 and F100 4 strokes have exhibited this same behavior ("making" oil). Same powerhead.<br /><br />There seems to be no fix for it yet. Yammy folks recommend running the engine harder for as long as it takes to get the rings seated better.<br /><br />Check the fuel pump diaphram for leaks, make sure the carb floats are not set too high and examine the crankcase breather valving.<br /><br />Good luck.

 

[fortran]

Re: 2003 Mercury 90HP 4-stroke crankcase oil level rises

Thanks. I'll ask the dealer that has it now about the following:<br />1) rich condition (altitude + stock jets?),<br />2) running the engine harder to seat the rings,<br />3) carb floats, and<br />4) crankcase breather valving.<br />The first dealer ruled out the fuel pump--replaced it twice.<br /><br />Bill

 

[fortran]

Re: 2003 Mercury 90HP 4-stroke crankcase oil level rises

The dealer ran the motor in a tank for two hours and reports that the oil level didn't rise, the oil didn't change color, and the oil didn't get thinner. They say they can't reproduce the condition. So, we agreed that I'd pick up the boat, lake-test it, take it back to them, and look at the oil together.<br /><br />I'm still concerned that neither Mercury or the two dealers have indicated that the primer bulb never getting hard is a problem. If there's gas in the gas tank, and the bulb's valves are working correctly, why doesn't the bulb get hard? Where would the gas go? Or, if the bulb's valves are not working properly, I understand that the bulb might not get hard, but what are consequences of a bad primer bulb?<br /><br />Thanks again,<br />Bill

 

[fortran]

Re: 2003 Mercury 90HP 4-stroke crankcase oil level rises

Wow! The dealer just called and told me Mercury is sending a new motor. The old one will go back to Mercury for analysis. Incredible service. Thank you, Mercury.<br /><br />Bill