Originally Posted by psneeld
Not an expert on transmissions, so I will just addd that American Diesel strongly advised about running the BW tranny cooler with coolant versus raw water.
They do have a kit or components and advice how to convert the engine oil cooler to coolant.
I have set up a few BW trannies on small detroits that actually have a cooler built in for the gear, using coolant. Sort of a necessity when keel cooling. This makes the tranny run hot, case gets to around 190F with IR gun. Not sure what the specs are for the gear, but these were commercial boats and run hard and had no issues with tranny at all.
The guts of a BW are really the same stuff as the guts of a car auto tranny, those get real hot in comparison.
I like gears cooled with coolant, the higher temps keep condensation out and oil stays nice and clean. And we know how many gears have been killed by sea water coolers leaking.
I suspect gear temp specs are often set considering SW cooling was being used, and there 190F is indeed hot. I can't see any reason the guts themselves are sensitive to 190F, and experience has backed that up.
The OP has a little gear with no cooling, probably a Hurth/ZF mechanical box. Those can be fitted with a "patch" cooler, but probably not necessary.