Chevrolet Duramax (badge, not an engine)

Duramax is a badge, not an engine. General Motors uses it for its diesels, and our rows show it across Chevrolet, GMC, Cadillac and Hummer — from a 1.6 four in the small crossovers to the 6.6 V8 in the heavy pickups.

The 6.6 V8 is what most people mean, and it is worth knowing that it is an Isuzu design — built by a GM–Isuzu joint venture, which is why some of its service literature reaches back to Isuzu rather than to GM.

Establish the RPO code, which is on the engine and in the build sheet: LB7, LLY, LBZ, LMM, LML, L5P for the 6.6, and quite different letters for the small ones. The generation decides everything, because the injectors, the emissions equipment and the known faults all changed between them.

⚑ The LB7's injectors are the family's famous fault — they fail internally and dilute the oil with fuel, and because they sit under the valve covers the job is far larger than an injector change on anything else here. An oil level rising on the dipstick is the tell, and it is the same warning as on every diesel in this catalogue for a different reason.

The later LML and L5P carry SCR and AdBlue, so their limp modes are as often an emissions sensor as an engine fault.