Cat Arrangement Numbers Ordering the Right Long Block

The model, such as C15, tells you the engine family. The serial number, with its prefix, tells you the specific build and the emissions era, since Caterpillar changed hardware over a long production run. The arrangement number goes further: it tells you the precise combination of parts and options used to assemble that engine, down to the turbocharger, oil pan style, and accessory drive.

Why the arrangement number matters: two engines can both be labeled C15, built in the same period, yet differ in real ways, such as turbo setup, oil pan shape, and sensor locations. Ordering by model alone can land you the wrong part. The arrangement number narrows things to the exact build, so the parts you order actually bolt on.

A long block is the major assembled core of the engine: the block, crankshaft, connecting rods, pistons, and cylinder head, without outer accessories such as the turbo, fuel system, and wiring harness. When buying a long block or a reman core, confirm all three numbers so the core matches the accessories you plan to bolt on.

How to find these numbers: the information plate, mounted on the block, shows the model, serial, and arrangement number. The ECM also stores engine data a technician can read with Cat ET. A Cat parts lookup uses the serial number, and often the arrangement, to pull the correct parts list.

For buyers: give the model, serial number with prefix, and arrangement number when you can, especially for long blocks, cylinder heads, and turbochargers. A good supplier cross-checks all three to avoid a costly wrong order.

A simple message for customers: the model tells the family, the serial tells the era, and the arrangement tells the exact build. Share all three with your supplier for a perfect match.