The medium duty Caterpillar 3126 diesel engine is designed for insertion into medium to large Cat machinery, like bulldozers, loaders, dump trucks and excavators. A second generation 3126 engine was developed in the late 1990s to integrate the HEUI fuel system (hydraulic electronic unit injection) and is known as the "B" series 3126.

Cylinder Style

Common in many diesel engines produced by Cat as well as Cummins, the 3126 Cat has an inline cylinder style. In-line motors tend to produce more torque vs horsepower, a key attribute for machines that require ample low-end engine power. Additionally, this engine introduced a new 3 valve system that revolutionized the way air passed through the cylinders -- boosting performance to nearly match entry-level heavy duty Cat engines.

Engine Size

This electronically controlled in-line diesel has a 7.2 liter displacement, outputting 300 horsepower at 2,200 RPM. Caterpillar also produces a high output version of the engine that produces 330 horsepower for recreational vehicles, emergency vehicles and fire trucks.

Unique Engine Components

Unique to the 3126, the engine drives the oil pump and air compressor via gears instead of independent electrical motors and has a re-grind-able crankshaft, all of which reduce weight and repair costs. The engine is equipped with steel connecting rods, dual thermostats and an isolated water pump. Additionally it has an electronic governor system to allow the machine RPMs to be regulated.

Original Versus “B” Series

The original 3126 is air-to-air aftercooled, but is not fuel injected via the HEUI system. The primary impetus for designing the "B" series was to conform to evolving EPA (environmental protection agency) restrictions regarding air pollution. The original 3126 is still manufactured for regions where the EPA restrictions are not enforced.