I just bought a 1 owner 350SDL, and it has the service booklet from new. It was changed with 15w40 oil at the dealership every 5k miles or so. However the last few changes in the booklet and the oil change sticker on the windsheild say 10w30. Too me that doesn't sound like a good idea and was planning on switching back to Mobil Delvac 15w40.

Any reason I shouldn't put diesel 15w40 back in it? I didn't know if their was some lighter weight oil theory with the 3.5Ls.

__________________
68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

There's quite a few discussions about this topic going on right now

My 350 SDL get Rotella T6 5w40. A 15w40 product is probably fine in the summer, but I wouldn't use it in the winter time.

10w30 is not an oil I would use in a diesel vehicle.

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.