Cummins B-series (5.9 / 6.7)

Cummins' inline-six diesel — in the Ram heavy-duty pickups since 1989, and briefly in the Nissan Titan XD.

⚑ It is an industrial engine in a pickup, and that is not marketing: the B-series was designed for agricultural and commercial use, and the version in a Ram shares its architecture with engines in tractors and generators. Its reputation for very high mileage follows from the design brief rather than from tuning.

An inline six is also why it sounds and behaves as it does — inherently balanced, with a single cylinder head and no V-angle, which makes it simpler to work on than any V8 diesel in this catalogue.

The 12-valve 6BT of 1989–1998 is mechanically injected and has no engine electronics worth the name; the 24-valve and the later ISB and 6.7 are common-rail with everything that follows. That line divides the family more than the displacement does.

Two recurring items: the VP44 injection pump on the 1998–2002 24-valve, whose failure is common and well documented; and on the 6.7, the emissions equipment — DPF, EGR and SCR — which is what most modern complaints are actually about. The engine underneath is rarely the fault.