First of all, can anyone remind me what the official spec in the manual is? My guess is NOT synthetic, but would like to know. I don not have an owners manual to look up.
Second of all, I run mobile1 0w40 on my E39 M5 per mobile1 website recommendation. I'm in Chicago, so below32F is quite common. That said, it would be nice to keep the same oil in my garage, but if anyone has any reason I shouldn't, or simply because that's not what the car "desires", please let me know.
Please, I know there is no absolute answer to my 2nd question, and I'm open to your opinions and comments. Especially if someone has a BAD example or data on using 0w40 on E34M5. BTW, it is 1991, with 110k miles.