Caterpillar C11

The Caterpillar C11 is an 11.1 L (677 cu in) inline-six, four-stroke diesel engine, not a standalone machine, built for on-highway trucks alongside a parallel industrial engine variant. It runs Cat's ACERT emissions technology with MEUI (modular electronic unit injection), a compound (two-stage, in-series) turbocharger arrangement, and a variable valve actuation (VVA) cylinder head, on a 130 x 140 mm (5.12 x 5.51 in) bore and stroke with roughly 17.2:1 compression. Published ratings across on-highway and industrial applications span about 242-336 bkW (325-450 hp) at 1,800-2,100 rpm, varying by rating and series. Net dry weight for the basic engine runs roughly 890-930 kg (1,965-2,050 lb) depending on configuration. Cat built the on-highway C11 from December 2003 through the 2006 model year, sold under several serial-number prefix families across engine and industrial builds. It slotted into Cat's 2000s truck lineup below the C13/C15, filling ground adjacent to the outgoing 3406E-based heavy-duty family as Cat moved its truck engines to ACERT; the C13 carried the smaller-bore ACERT on-highway slot forward after C11 production ended. Configurations included multiple horsepower and torque ratings for linehaul and vocational chassis, plus industrial packages such as dry-manifold builds for well-service and stationary power applications.

The C11 arrived already in ACERT trim, so unlike the mechanical-injection engines it followed in Cat's lineup, there is no naturally-aspirated or pre-electronic prior generation of this exact engine. The changes that did happen during its short run were mostly calibration and electronics: horsepower/torque spreads tuned by application, and running refinements to VVA solenoid control and injector-driver electronics as Cat matured ACERT calibration through 2004-2006. Because on-highway production stopped after 2006, the C11 is a shorter-lived, transitional engine compared to the C13/C15/3406E family that bracketed it. In today's used and parts market it turns up mainly in mid-2000s Class 8 daycabs, mixed-use vocational trucks, and industrial packages that stayed in service into the following decade. Lower production volumes and only partial parts commonality with the C13 (shared architecture, not identical parts) make rebuild kits, injectors and VVA components harder to source than for the higher-volume C13/C15, which keeps good running cores and low-hour take-outs in steady demand from owners keeping C11-powered trucks on the road.

Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.