transmission oil change

I everybody
lately i got puzzled by two yanmar manual on the same motor ...
one says to change transmission oil every 250 hours ...
the other every 1000 ...
what do you think??

 

Such intervals are often ruled by commercial interests, especially if a specific brand of oil is recommended.
There hardly is a technical reason to ever change transmission oil at all, just check the oil level regularly. Only if the oil has changed color or feels gritty between your fingers it is time to drain the oil and investigate the cause.
One possible exception are transmissions using ATF. That is a hygroscopic fluid, collecting water through the vent on top of the transmission. If the engine is used infrequently and never reaches a decent operating temperature the gearbox fluid deteriorates and needs to be changed every few years.

 

i think it would mean 250 for engine , 1000 for trans.

 

Depends on the type of transmission. If it is a Hurth or similiar brand that uses friction plates it should probably be changed every couple hundred hours or yearly if just weekend use.

 

on auto engines, depending on type, they typically want oil changes in the equivalent of 100 to 200 hours of run time (5 to 10k miles). And for both manual (uses heavy gear oil) and Auto trans (Uses ATF) they want the equivalent of 600 to 750 hours (about 30k miles). Most people run them much longer without ill effect, and almost no one changed the rear diff oil even though that is recommended at the same interval.

With the damp environment in most boat hulls it is difficult to imagine why they would use a longer change interval. Less dust and dirt in the air perhaps? Boats often sit for long periods of time without usage, so moister build-up would be a problem I would think.

If this particular engine is known to have trouble because of infrequent oil changes than it might save you money to use the lower change interval. But as already noted, these intervals are mostly a way to get more money out of their customers, if the oil level is good and it is still "slippery", it is still good to use.

 

I change engine oil at 200 hrs and transmission oil yearly. I generate about 750 hrs per year on the powerplant. Do you need to change the transmission oil ? I have no idea...the oil I remove is always perfectly clear and the screen filter is always clean. The positive aspect of changing the gearbox oil is "general maintenance".. the oil change forces you to get down on your hands and knees for a half hour and observe the general rear engine condition. Chafed hydraulic hoses, weeping oil coolers, loose fasteners....become obviuos. This is the same reason why you change front end vee belts every 2 years....inspection. Oil is cheap...do it.