Where inboard
engines, either gasoline or diesel, are used to
drive pleasure craft or small commercial boats,
there will be a wide variance in the lubricants
used in the transmissions. This is due to design differences. Therefore,
the lubricating fluid recommended may be an EP
gear oil or a straight mineral oil falling
within the SAE 90, 140 or 250 viscosity range, a motor oil, or
an automatic transmission fluid. The lubricant for the
reduction gears may be supplied under pressure from the
engine oil system or an independent oil system for the
gears alone may be provided. The lubricant then
will no doubt be an SAE 50 oil for
summer and an SAE 30 or 40 for winter operation. With
separate lubricating system for the gears, the
corresponding oils may be an SAE 140 or SAE 90.
The fluid
used in a hydraulically shifted transmission must serve as
a hydraulic medium for a complex control
system and also act as a lubricant and heat transfer medium.
This, then points to the use of ATF. In addition to the transmission,
which provides for reversing, neutral, and forward speed, in large boats, a
further reduction gear unit may be found. It may even be that the former gears
may be lubricated from the engine and the latter require the heavy gear oil.
Due to the variations in
drives and methods of lubrication, the supplier of the engine is in the best
position to recommend the proper lubricant for gear trains.
