I agree with Ian Munro -- I was using Dextron III in my Velvet Drive transmission; however, after reading other TWL posts and the advice of others that have similar boats in the Pacific Northwest I changed to Mobil Synthetic ATF last year. The added cost of Mobil Synthetic ATF is a good investment. The transmission shifts a lot smoother and is probably running cooler but I never took readings before and after readings. Al Pacific Trawler 37 "Pleasant Moment" Palm Coast, Florida