Caterpillar 3612

The Caterpillar 3612 is a heavy-duty, medium-speed V12 diesel engine built primarily as the prime mover for large diesel generator sets, with parallel use in mechanical-drive and marine propulsion packages. It uses the Cat 3612 engine itself: a turbocharged, aftercooled, direct-injection V12 with a 280 mm bore and 300 mm stroke and roughly 221.6-221.7 L of displacement, running at rated speeds between about 720 and 1,200 rpm depending on the 50 Hz/60 Hz and pole configuration selected. A bare engine weighs on the order of 25,000-26,000 kg (55,000-58,000 lb), while a fully packaged generator set with alternator, skid, and cooling commonly runs 50,000-60,000+ kg (110,000-134,000+ lb) depending on options - the range is wide because enclosure, radiator versus remote cooling, and duty rating change the package substantially. The engine belongs to Caterpillar's 3600 family, introduced in the mid-1980s alongside the smaller 3606 and 3608 and the larger 3616, all sharing the same bore, stroke, and basic architecture; the 3612 has stayed in Cat's catalog continuously since, with used and remanufactured units dating back to the late 1980s still active in the field. It is offered in mission-critical, continuous, prime, and standby power ratings, and marine variants are marketed under the Caterpillar Motoren C280-12 name for IMO/emissions-tier compliance.

Across its long production run the 3612 platform has moved from mechanical governing and unit injection toward more electronically managed fuel and speed control on later builds, and marine/offshore variants picked up IMO Tier compliance branding without changing the core bore-stroke architecture shared across the 3600 family. Power ratings have also been extended over time as Caterpillar broadened the speed and frequency options offered on the genset package, so two 3612 units of different vintage can carry meaningfully different control systems and output ratings even though the base engine looks the same. That long, largely stable production run is exactly why the 3612 still matters in the used and parts market: it is a mechanically straightforward, high-output medium-speed diesel with a deep base of running hours in oilfield, marine, and continuous/mission-critical power applications, factory and aftermarket parts support remains strong, and the long overhaul intervals typical of this engine family mean a used unit can still carry tens of thousands of hours of remaining service life before a major rebuild is due.

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.