Soon I'll do an oil change for the first time on my recently acquired 1988 745 Turbo. The owner's manual says the engine holds 4.0 quarts (same as my old 245DL B21F), but that an additional 0.7 quarts should be added if the oil cooler is drained. Is there some extra step that has to be taken to drain the oil cooler - like if there is a valve or something that keeps the oil in the cooler until there is sufficient pressure to push it through? Or should I just add 4.0 quarts and then add a bit more based on the dipstick level?

Zack
1980 245DL M46 272k
1988 745T+ M46 189k

Just add 4 quarts; don't bother with the oil cooler.
There's a thermostatic valve which opens when the oil is sufficiently hot, which I believe it hardly ever is, and yes, you have to disconnect an oil line to drain the cooler.
Turbos have enough oil leakage issues without having to get the hose connection to seal after every oil change.
--
Jim McDonald

I've wondered this myself, the book is not much help. I think that all the oil drains into the pan even with the cooler so I've been changing the oil like normal, and I always buy 5 qts. just to be sure. You have to get under the car to get the filter so that kinda sucks. I'm changing my oil this wknd too.

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Blue760t