False Overheating Alerts on Komatsu PC300 During Cold Start

[MikePhua]

A Komatsu PC300 showing overheating warnings immediately after a cold start is most likely experiencing an electrical fault rather than a true thermal issue. This behavior often stems from wiring damage, sensor misreads, or grounding errors that trigger false alerts before the engine has even warmed up.
Machine Background and Cooling System Design
The Komatsu PC300 is a heavy-duty hydraulic excavator used in mining, road building, and large-scale earthmoving. It features a robust cooling system with a belt-driven water pump, thermostatic control, and a multi-core radiator. The engine control module (ECM) monitors coolant temperature via sensors and displays readings on both a gauge and a warning light. These systems are designed to alert operators to overheating risks, but they rely entirely on electrical signals.
Terminology and Component Overview

• Coolant Temperature Sensor: Measures engine coolant temperature and sends data to the ECM and dashboard.
  
• Wiring Harness: Bundled electrical cables that connect sensors to the ECM. Vulnerable to abrasion and heat damage.
  
• Ground Fault: An unintended electrical path to ground, which can distort sensor readings.
  
• Idiot Light: A warning light that activates when a preset threshold is exceeded, often without precise data.
  
• IR Temp Gun: Infrared thermometer used to verify actual surface temperatures independently of the gauge.
  

Diagnostic Observations and Field Insights
Operators have reported that the PC300 can trigger a “hot coolant” warning within two minutes of startup, even when the engine is cold and under no load. In one case, a technician traced the issue to a chafed wire in the engine harness that had shorted against a clamp. This caused the sensor signal to ground prematurely, forcing the gauge to read full hot and activating the warning light.
Another operator used an IR temp gun to confirm that the engine block and radiator were still below 100°F when the alert appeared. This ruled out a mechanical failure and pointed to an electrical miscommunication.
Recommended Troubleshooting Steps

• Inspect the wiring harness along the engine block for signs of wear, pinching, or melted insulation.
  
• Test the coolant temperature sensor with a multimeter. Even new sensors can be defective or improperly calibrated.
  
• Check for proper grounding at the sensor and ECM. Loose or corroded grounds can cause erratic readings.
  
• Use an IR temp gun to verify actual engine temperature during startup.
  
• Confirm whether the gauge and warning light are triggered by separate sensors or a shared signal. Some models use dual inputs.
  

If the sensor and wiring are intact, the issue may lie in the ECM or dashboard logic. In rare cases, low coolant levels or a stuck thermostat can cause localized overheating, but this typically occurs after several minutes of operation—not immediately.
Preventive Measures and Long-Term Solutions

• Secure wiring harnesses with heat-resistant clamps and protective sheathing.
  
• Replace sensors with OEM parts to ensure compatibility and accuracy.
  
• Log temperature readings during startup and compare with gauge behavior.
  
• Update ECM firmware if available, as some Komatsu models have known calibration bugs.
  
• Train operators to verify overheating alerts with secondary tools before shutting down the machine.
  

Conclusion
Overheating warnings on a cold-started Komatsu PC300 are rarely caused by actual thermal overload. Instead, they reflect electrical faults that mislead the monitoring system. By inspecting the wiring harness, validating sensor output, and using independent temperature checks, technicians can resolve these false alerts and restore confidence in the machine’s diagnostics.