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
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
Bill in Omaha
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
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
Thank you Fred W. If the Chevron stuff is cheaper than the BMW brand,
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