The 15W-40 grade seems to be unique to the CI-4 rated HD diesel engine oils. Though I DO use 15W-40 Chevron Delo in my vintage cars that do no not have catalysts due to its higher concentration of detergent, dispersant, anti-wear, and anti-corrosion addtives, I DO NOT use Delo in my "modern" cars with catalysts including my 190. For these cars I use a conventional API SL 20W-50.

Modern cars do not need the additional additive concentration from the CI-4 oils because they have precise fuel control, which reduces crankcase dilution. Also, some of these additives are not kind to catalysts. Given that oil consumption increases with age and the 103 engines are already on the ragged edge of CA's ASM emission test, I continue to use SL oil in my Mercedes and recommend this practice to other owners.

On balance, I believe the potential pitfalls of using CI-4 oils in these cars outweighs the potential benefits.

Duke