All vehicle manufacturers compromise on engine oil recommendations

Low viscosity is good for fuel mileage ratings, thus BMW’s primary 5W-30 recommendation allows BMW to advertise higher mileage figures, but is deleterious to engine wear which is greatly reduced when using the higher viscosity 15W-50 oil. The knowledgeable Consumer has to make the choice of mileage vs. engine longevity.

Likewise, the availability of specifically formulated diesel engine oils to the motoring public through service stations or “Quick Lubes” is problematic because the motoring public is not aware of them, therefore don’t ask for them, therefore the product is not inventoried.

Yes, gasoline engine oils have “some” of the attributes necessary for use in diesel engines and because they are more readily available (thus recommeded by BMW) can be used, but as with the viscosity statement above the knowledgeable Consumer has to make the choice.

Diesel engines are relatively low revving extremely high compression high torque engines which burn relatively (compared to gasoline) high sulfur content diesel fuels. In the USA lower cost diesel #2 (also known as “railroad diesel”), which has a high paraffin/sulfur content which “gels” at low temperatures, is marketed to the motoring public during the summer months. Higher cost diesel #1 (also known as kerosene which when highly filtered becomes aviation jet fuel) has much more of the paraffin/sulfur refined out and is marketed during winter months (doesn’t “gel” at low temperatures). It is the relatively high sulfur content of diesel fuel (European diesel is cleaner, i.e. has less sulfur than that in the USA) as compared to gasoline which presents the greater problem for diesel engine oils.

The higher sulfur content of diesel fuel vs. gasoline results in much more sulfur being “blown by” the piston rings as hydrogen sulfide (H2S) which when exposed to water in the crankcase becomes sulfuric acid (H2SO4). Diesel engine oils have to cope with this relatively greater sulfuric acid content and are formulated to do so by having a greatly increased “Total Base Number” (TBN), which is equivalent, to having more “Tums” available for the crankcase acid indigestion.

That being said, I personally would only use an engine oil formulated specifically for diesel engines.