3126B Marine Engine Caterpillar

• Four-stroke cycle

• Direct fuel injection

• Hydraulically actuated electronic unit injection

• Turbocharging

• Raw/seawater aftercooling

Engine Specifications

Note: The front end of the engine is opposite the flywheel end of the engine. The left side and the right side of the engine are determined from the flywheel end. The number 1 cylinder is the front cylinder.

Illustration 1	g00574598
Cylinder and valve location (A) Exhaust valve (B) Inlet valve

Electronic Engine Features

The Cat 3126B Marine Engines are designed for electronic controls. The integral on board computer controls the operation of the engine. Current operating conditions are monitored. The Electronic Control Module (ECM) controls the response of the engine to these conditions and to the demands of the operator. These conditions and operator demands determine the precise control of fuel injection by the ECM. The electronic engine control system provides the following features:

• Engine Monitoring

• Engine speed governing

• Automatic air/fuel ratio control

• Torque rise shaping

• Injection timing control

• System diagnostics

For more information on electronic engine features, refer to the Operation and Maintenance Manual, "Engine Features and Controls" topic (Operation Section).

Hydraulic Electronic Unit Injectors

Hydraulically Actuated Electronic Unit Injectors (HEUI) perform the following functions: pumping of fuel, fuel metering and injection timing.

The unit injectors are controlled by the ECM. The ECM uses the camshaft position and the engine speed signals from the engine speed/timing sensors and the inlet air pressure sensors. The rated rpm of the engine is identified on the Information Plate.

Engine Diagnostics

The engine has built-in diagnostics in order to ensure that all of the components are functioning properly. In the event of a deviation from the programmed limits, the operator will be alerted to the condition by a "DIAGNOSTIC" lamp. Under certain conditions, the engine horsepower and the vessel speed may be limited. A Cat electronic service tool may be used to display the diagnostic code.

Diagnostic codes are logged and stored in the ECM. For additional information, refer to the Operation and Maintenance Manual, "Engine Diagnostics" topic (Operation Section).

Engine Speed Governing

The ECM provides electronic governing that controls characteristics of fuel injection in order to maintain the desired engine rpm. The functionality of electronic governor is similar to the Cat mechanical governor, but the electronic governor includes additional features.

Engine Cooling and Lubrication

The cooling system consists of the following components:

• Centrifugal pump that is driven by belts

• Water temperature regulator which regulates the engine coolant temperature

• Oil cooler

• Auxiliary water pump

• Raw/seawater aftercooling

• Heat exchanger

The engine lubricating oil that is supplied is cooled. The engine lubricating oil is also filtered. Bypass valves provide unrestricted flow of lubrication oil to the engine components during the following conditions:

• High oil viscosity

• Plugged oil cooler or plugged oil filter elements (paper cartridge)

Marine Transmissions

Several manufacturers of marine gears offer marine transmissions through local distributors. Lubrication oil for the marine transmission can be cooled by an optional engine mounted transmission oil cooler (certain engine ratings).

Engine Service Life

Engine efficiency and maximum utilization of engine performance depend on the adherence to proper operation and maintenance recommendations. In addition, use recommended fuels, coolants, and lubricants. Use the Operation and Maintenance Manual as a guide for required engine maintenance.

Expected engine life is generally predicted by the average power that is demanded. The average power that is demanded is based on fuel consumption of the engine over a time. Reduced hours of operation at full throttle and/or operating at reduced throttle settings result in a lower average power demand. Reduced hours of operation will increase the length of operating time before an engine overhaul is required. For more information, refer to the Operation and Maintenance Manual, "Overhaul Considerations" topic (Maintenance Section).