How to identify a Cummins engine before ordering parts

Most wrong parts are ordered against an engine model and nothing else. The model is a family, not a specification. Cummins built the same model over long production runs and in several configurations at once, for trucks, gensets, marine and construction, and the parts that hang off the block change between them even when the block does not.

Three pieces of information identify an engine properly: the model, the engine serial number, and the CPL. Between them they describe not just which engine you have but which build of it.

The dataplate is a narrow metal tag, and on most engines it is fixed to the gear housing or front cover. It carries the model, the serial number, the CPL, and the horsepower and speed rating the engine left the factory with.

Plates go missing. They get painted over, knocked off during a rebuild, or corroded past reading on a set that has stood outside. If the plate has gone, the serial number is usually stamped into the block itself. On many engines that stamping is on the left side of the block seen from the front, above the oil cooler housing.

If you find nothing on either, photograph the engine from the front, the side and the top, and send that. The castings, the pump, the manifold and the filter head arrangement between them usually narrow it down.

The engine serial number, usually shortened to ESN, belongs to one engine and no other. Older engines carry eight digits. Newer ones run to longer alphanumeric strings.

It is not the same as a part number, and it is not the genset's serial number. A generating set has a serial and a model of its own on the set's nameplate, separate from the engine inside it. When you send us details for a genset, both are useful, because the same engine goes into sets of more than one rating.

CPL stands for Critical Parts List. It is a short number, four or five digits, that covers every engine built to the same specification: the same pistons, the same injectors, the same camshaft, the same fuel setting.

This is the number that separates two engines wearing the same model name. Two 6BTs of the same year can take different injectors and different pistons, and the CPL is what tells you which. When a parts counter asks for the CPL rather than the year, this is why.

The number stamped or cast onto the part you are replacing beats everything else, because it identifies the part directly rather than by inference. Send that first if it is readable.

Where it is not, send the engine model, serial number and CPL off the dataplate, and say what the engine is installed in. A photograph of the old part next to a tape measure is worth more than a written description, particularly for pumps, coolers and hoses, where variants differ by a mounting face or a length rather than by anything you could put into words.