Yanmar SD 20 saildrive problem
 

I have a problem with the saildrive on my 3GM30 that perhaps someone else
has experienced.

On two or three occasions (always wintertime, southern Chesapeake Bay) I
have found perhaps 2 or 3 ounces of transmission oil that somehow leaked out
up top somewhere and ends pooled up on top of the rubber diaphragm seal. The
first time, last winter, there was some water in the oil, which was Amsoil
synthetic..

The only possible cause I could come up with is that when the temperature
drops the oil--and air--inside the saildrive contract, and since it is
unvented, creates a partial vacuum that draws water past the prop shaft
seals. I know that water down at the bottom of the saildrive won't freeze
(while still in the water) but perhaps there is water mixed with the oil
that is up above the hulll bottom, and this freezes and expands.

Still don't know where the oil escaped, although what I found this week
before hauling would have come out of the fill hole as I now leave the cap
loose in the wintertime when not operating to prevent a vacuum drawing in
more water After hauling, and draining the oil there doesn't seem to be
water in the oil, which had been changed over to petroleum.

Since it appears there is no water intrusion this time, another thought just
came to me. Could it be that the aluminum saildrive contracts with
temperature more than the oil does, forcing out the oil? I have no idea what
the coefficient of expansion for oil is, but I know Al is pretty high.

Anybody have an experience like this?

Thanks for any thoughts or suggestions.

Garland