M25: recommended oil-change interval?

According to the date and run-hours numbers I wrote on the side of my oil filter with a Sharpie, I've run my M-25 a little less than 50 hours since last changing the oil in 2017.

I have "check/change oil" on my spring list every year, but didn't do it last year because... well, the oil only had about 10 hours on it, and that seemed sorta silly.

Looking at the number last night got me wondering... is there a "right" interval? I have "100 hours" stuck in my head, not sure where it came from, but it might take several years for me to rack up 100 hours on the clock.

Should it be done once a year, or 100 hours, whichever comes first, or...?

Bruce

Hi Bruce,

That is a common issue for sailboats that don't use their engine much. I have the Universal 16 hp diesel engine, and my manual says change oil every 100 engine hours or annually. But you're right that it doesn't make sense to change it after only a few hours. I routinely change the oil at about 75 hours, so sooner than they recommend (it's a fairly cheap way to prolong the engine life), and in the interim I check the oil regularly for colour/clarity and for lubricity feel between my thumb and finger. It will always go fairly dark right away because it's a diesel, but I can tell the difference when it gets quite black vs when I can still see the fill mark on the dipstick.

There is a common caution to not leave oil in the engine for too long as the acids in used oil is not good for the engine over the winter or for long periods, but again, with only a few hours on the engine after the last change, you won't have much acid in there.

If you only have 10 hours on the engine, I would not change it. At 50 hours, if it's been a year since the last oil change, I would tend to change it to prolong the life of the engine, though I'm sure it could go to 75 hours without a problem. That's my opinion, based on my 16 hp engine and my tendency to baby it. I'll be interested in what others suggest.

Frank

I change the oil every winter regardless of how many hours are on the motor, that way it sits during its least used time with fresh oil in it. I put on 50-100 hours a year which happens to be right around the interval anyways.

With a mityvac fluid extractor it's so easy I should actually change it in the spring as well (and because I find you cannot get all of the old oil out with the extractor anyways.)