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CAT 315L Excavator Overview
The Caterpillar 315L hydraulic excavator was introduced in the mid-1990s as part of CAT’s compact crawler lineup. Designed for urban construction, utility trenching, and light demolition, the 315L featured a turbocharged diesel engine producing approximately 110 horsepower, an operating weight of around 33,000 pounds, and a dig depth exceeding 20 feet. It was equipped with a mechanical fuel injection system and open-center hydraulics, making it reliable and relatively easy to service.
Caterpillar Inc., founded in 1925, had by the 1990s become a global leader in earthmoving equipment. The 315L was part of its strategy to offer mid-size excavators with simplified electronics and robust mechanical systems. Thousands of units were sold across North America and Asia, and many remain in service today.
Rebuilding the Injection Pump and Governor Adjustment
When the injection pump on a CAT 315L is rebuilt, it’s common for technicians to make slight adjustments to the governor. The governor regulates fuel delivery based on engine load and speed, and any change in its calibration can affect engine response. If the machine begins to “lug down” or lose RPM under load—especially during digging—it suggests that the pump and governor are not properly synchronized with the engine’s control system.
Why Calibration Is Necessary
Calibration ensures that the injection pump delivers the correct amount of fuel at the right time, matching the engine’s RPM curve and load demands. Without calibration:
Terminology Notes
In one case, a rebuilt pump and new injectors resolved engine flutter, but the machine began overheating after 30 minutes of operation. The coolant temperature reached the red zone, then cooled within five minutes at idle. Hydraulic oil temperatures were measured at 162°F in and 149°F out, suggesting normal flow through the cooler.
Despite cleaning the radiator and confirming airflow, the machine continued to heat up. Temperature readings showed:
A rebuilt injection pump on a CAT 315L must be calibrated to restore full engine performance and prevent lugging under load. Cooling issues that arise afterward may be unrelated but should be addressed through thorough inspection of the radiator, fan, and hydraulic system. With proper calibration and cooling maintenance, the 315L can continue operating reliably in demanding conditions.
The Caterpillar 315L hydraulic excavator was introduced in the mid-1990s as part of CAT’s compact crawler lineup. Designed for urban construction, utility trenching, and light demolition, the 315L featured a turbocharged diesel engine producing approximately 110 horsepower, an operating weight of around 33,000 pounds, and a dig depth exceeding 20 feet. It was equipped with a mechanical fuel injection system and open-center hydraulics, making it reliable and relatively easy to service.
Caterpillar Inc., founded in 1925, had by the 1990s become a global leader in earthmoving equipment. The 315L was part of its strategy to offer mid-size excavators with simplified electronics and robust mechanical systems. Thousands of units were sold across North America and Asia, and many remain in service today.
Rebuilding the Injection Pump and Governor Adjustment
When the injection pump on a CAT 315L is rebuilt, it’s common for technicians to make slight adjustments to the governor. The governor regulates fuel delivery based on engine load and speed, and any change in its calibration can affect engine response. If the machine begins to “lug down” or lose RPM under load—especially during digging—it suggests that the pump and governor are not properly synchronized with the engine’s control system.
Why Calibration Is Necessary
Calibration ensures that the injection pump delivers the correct amount of fuel at the right time, matching the engine’s RPM curve and load demands. Without calibration:
- Fuel delivery may lag, causing poor throttle response.
- Engine RPM may drop under load, reducing hydraulic performance.
- Computer-controlled systems may misinterpret signals, triggering fault codes or warning lights.
Terminology Notes
- Injection Pump: A mechanical or electronic device that meters and delivers fuel to the engine cylinders under pressure.
- Governor: A control mechanism that adjusts fuel delivery based on engine speed and load.
- Calibration: The process of adjusting mechanical or electronic components to match factory specifications.
In one case, a rebuilt pump and new injectors resolved engine flutter, but the machine began overheating after 30 minutes of operation. The coolant temperature reached the red zone, then cooled within five minutes at idle. Hydraulic oil temperatures were measured at 162°F in and 149°F out, suggesting normal flow through the cooler.
Despite cleaning the radiator and confirming airflow, the machine continued to heat up. Temperature readings showed:
- Thermostat housing: 202°F
- Top radiator hose: 194°F
- Bottom hose: 179°F
- Partially blocked radiator cores, even if visually clean.
- Damaged or missing shrouds, reducing airflow.
- Incorrect fan installation, though in this case the fan was confirmed to be correct.
- Calibrate the Injection Pump After Rebuild: Use factory specs or a qualified technician to match fuel delivery to RPM.
- Verify Cooling System Efficiency: Measure temperature drop across the radiator and inspect airflow components.
- Check Hydraulic Heat Transfer: Ensure the oil cooler is not contributing excess heat to the engine.
- Inspect Temperature Sensors: A faulty sensor may trigger false warnings.
- Split and Clean Radiator Package: Even if the exterior is clean, internal debris may reduce cooling efficiency.
A rebuilt injection pump on a CAT 315L must be calibrated to restore full engine performance and prevent lugging under load. Cooling issues that arise afterward may be unrelated but should be addressed through thorough inspection of the radiator, fan, and hydraulic system. With proper calibration and cooling maintenance, the 315L can continue operating reliably in demanding conditions.
