Though automakers like Stellantis, Mazda, BMW, and Mercedes-Benz are keeping a few straight-six engines alive in 2025, there are currently just two straight-six diesel powerplants left on the market.

If you've ever opened up a BMW's hood before, chances are you're either looking at a V8 or a straight six. The latter configuration has become something of a de facto trademark for the marque, with ...