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Overcooling
25. Defective Temperature GaugeIf the temperature gauge shows that the coolant temperature is below normal and all other conditions indicate that conditions are normal, check the coolant temperature in another method, such as:* Read the coolant temperature with an ECAP or DDT.* Install an 8T0470 Thermistor Thermometer Group* Install a temperature sensitive tape.* Install a new gauge that is known to be good.26. Defective Coolant Temperature SensorIf a fault is detected in the coolant temperature sensor circuit, determine if the fault is in the wiring or the coolant temperature sensor following the procedure in Electronic Troubleshooting, 3176 Diesel Truck Engine, Form No. SENR3913. Repair or replace parts as needed. The coolant temperature sensor should be accurate within plus or minus 3° C (6° F). Check the accuracy of the sensor if it is found to be out of specification.27. Long Idle PeriodsRunning the engine for extended periods of time under no load conditions will cause the engine heat to be removed at a faster rate than it is being generated.28. Very Light LoadsVery light loads, very slow speeds, or downhill travel can cause below normal heating due to the decreased amount of fuel that is being burned. The installation of shutters will help correct this problem by decreasing the flow of air into the engine compartment.29. Defective Water Temperature RegulatorIf the water temperature regulator is stuck open, it will cause below normal engine heating. To test the thermostat, see the topic, Testing The Cooling System, in the Testing and Adjusting section of Systems Operation, Testing and Adjusting, Form No. SENR3909.30. Faulty Fan Clutch (Will Not Disengage)Check for proper operation of the fan clutch. Refer to the Truck Manufacturer's Service Manual for the proper procedure.31. Vent Line OpenIf the vent line (OEM) between the temperature regulator and the radiator top tank is open, overcooling could result. Install a valve assembly in the line that will allow air venting but restrict coolant flow with the engine running.