One can readily see that it might be necessary to remove heat from the transmission oil
, particularly on those transmission
designs that employ hydraulic pressure to activate the clutch
packs as opposed to mechanically activated clutches. The question is why would a designer
choose to use sea water cooling
as opposed to freshwater cooling to remove that heat?
One of the most important factors in heat transfer is the "delta T" of the two fluids, that is, the difference in temperature between the fluids. The greater the temp difference, the greater the heat transfer rate.
An engine designer
usually uses a maximum sea water temperature of about 90 degrees F. for heat transfer calculations, and then builds some additional safety
factor into the mix to account for fouled tubes, thruhulls, etc. His calculation might use a delta
T where the transmission fluid is running at 220 degrees F and the sea water used to cool it is 90 degrees F. Using these numbers he comes up with a cooler of a certain size and cools his oil
temp down to 200F.
Contrast this to a calculation where the transmission fluid is the same 220 F but the antifreeze
flowing to the cooler has just come out of the engine heat exchanger
at 160F. You can see that the size of the transmission cooler required is going to be much larger than in the case of the sea water cooled example.
So the answer to your question is that you can change your cooling medium, but probably you will have to increase the size of the gear
cooler that you have inorder to adequately cool the transmission.