Originally Posted by Capt.Bill11
Exactly. And since its splash lubed there should be no need to over fill the transmission. Especially since when the transmission is not under pressure the oil in the cooler would in most cases drain back into the transmission. So the fluid would be over filled some what anyway.
My guess is the system is fine as is. No extra oil or cooling needed.
Your guess is not agreeing with recommendations of some marine transmission manufacturers:
Ie - (From “Velvet-Drive”:
It has been determined by tests and practical experience that all Velvet Drive marine transmissions call be free-wheeled without risking damage in sailing or trolling applications. Caution should be taken to be sure that proper oil level is maintained prior to freewheeling as well as normal running. Freewheeling one propeller of a twin engine boat at trolling speeds will not cause damage to the transmission connected to the freewheeling propeller.
Extended periods of free-wheeling at high speeds may cause the transmission to overheat; therefore, it is recommended that transmission sump temperature be monitored and free-wheeling discontinued whenever 230 degrees F or 111 degrees C is reached.)
In this case the presumption is that the propeller shaft is driven by the auxiliary engine with speed higher then "trolling speed" more than 3knts for extended period of time.
On MG-509 the recommendation is not to freewheel over 8hrs.
But again, it's your boat you can experiment as much as you'll like.