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STEP 1
Perform a visual inspection of the engine and cooling system. Top off the coolant level if it is low.
STEP 2
Because a diesel engine will not reach operating temperature if it is only run at idle, the engine needs to be placed under load and run until the cooling system temperature no longer increases. Alternatively, the engine can be operated at high idle for 45 minutes.
STEP 3
After reaching maximum operating temperature, aim a noncontact infrared (IR) temperature gun at the thermostat housing and record the temperature.
STEP 4
If the engine is equipped with an on/off engine fan, also record the coolant temperature at which the fan is activated and deactivated to validate correct fan operation.
STEP 5
Using an EST, such as a scanner or OEM software, observe and record the engine coolant temperature parameter data provided by the temperature sensor.
STEP 6
Compare the IR thermometer reading with the coolant sensor data to check whether the sensor data is valid and accurate. Also compare the data with the instrument cluster display to verify the correct gauge operation.
STEP 7
If the engine is equipped with an electronically controlled, variable-speed engine fan, activate the cooling fan using OEM software to verify that the fan is operating correctly.
STEP 8
Report your results and provide service recommendations for further repairs or diagnosis.
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