Hello,
I've got a gallon of Rotella 15W-40 oil hanging around my garage, used to use it in my engine but have since switched to Mobil 1 Turbo Diesel Truck for easier winter starts (I live in Maine). Since I have no other use for it, I wonder if it would be suitable to use as transmission fluid in my 240D's 4-speed manual transmission. I've done some searches, and it looks like it's about the heaviest oil you'd want to use for that application. On the plus side, seems like it might make the transmission quieter at highway speeds. Right now it has 5W-20 in it, and at 65+ MPH it becomes difficult to carry on a conversation with passengers, especially ones in the back seat. (I realize it could just as easily be the driveshaft or differential, but that's another can of worms.) Could using heavier oil in the transmission cause any problems in cold weather?

Thanks,
Nate

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1985 300DT, Classic White, California, 175K
1984 300TD, Classic White, Euro, 285K


"When nine hundred years old you reach, look as good you will not. Hmm?" - Yoda