oil question, sorry

E36 it's good. M3, not so much. RTFM

15W-40 IS what my (Bentley) handbook recommends.

But the Chevron stuff is "formulate for diesels" - 15W-40 is 15W-40 right? Whether for diesel or gasoline engines, but I just want a sanity check.

Alrighty then, 15W40 it is.

Yeah, the diesel stuff undergoes different testing and ratings for use in the relatively dirty conditions of a diesel engine. I use Rotella T

15W40 in my E36 325i. It seems to like it just fine.

I do not believe the Bentley manual "recommends" 15w40, if it does, I did not find the reference.

I see on page 20-8 a chart that gives oil recomendations based on temperature, and 15w40 is suitable for a range from -10C to above 30C (about

15F to above 85F). Instead of the diesel formula, why not use 10w40? It will protect to the same high end of the scale, and colder than the lower end. The more critical spec to observe is the API service of SH or SJ. If the diesel formula meets these specs, then it ought to be okay.

I note that page 91 of the Owner's Manual ('94 3 Series) has a similar chart, but it includes 10w40, where the Bentley manual does not.

My '86 535i likes the thicker 15w-40. It does run warmer where I live (Omaha, NE to occasions at the Gulf in MS), especially in the summer. (Yeah, but it's a dry heat!) I hear the newer gas engines are tending towards lower viscosities.

Bill in Omaha '86 535i

Isn't Diesel engine oil very highly detergent to remove / keep in suspension all the soot from the blow-by on the OLD smokies? Shell Rotella was the original high detergent diesel lubricant back in the 50s and 60s

Conventional 10W40 is not a great choice. It has too much of the viscosity improvers that allow it to flow like a 10 weight oil when cold and still maintain 40 weight viscosity when hot. Those same improvers are more subject to shearing and viscosity breakdown with use. What was a 10W40 acts like a 10W30 after about 500 miles of use and is more like a 10W20 after 2000 miles.

15W40 diesel oil is actually a better bet.

Oy-oy-oy. OK, The Bentley manual actually says

"The fluids and lubricants specified by BMW are listed in Table e. Shown below is engine oil viscosity (SAE grade) vs. operating temperature range for the BMW engines covered in this manual."

For my temperature range (0-40 degrees C, Arizona), I would call that a fairly ringing recommendation, even though it doesn't use the actual word "recommendation".

Thank you Fred W. If the Chevron stuff is cheaper than the BMW brand, it's on.