- Engine:
- C15 (S/N: BXS1-UP)
A customer may assume that the C15 On-highway Engine may not be at minimum operating temperature in cold weather, or the engine may be operating below the minimum operating temperature. The minimum operating temperature is 71 °C (160 °F) when the engine is at idle. The minimum operating temperature is 80 °C (175 °F) while the engine is running down the road.
Overcooling is defined as excessive heat loss from the engine system. The excessive heat loss does not allow the engine to reach normal operating temperatures. The engine will input heat into the system from the cylinder liners and from the cylinder head assembly. The amount of heat in is a variable that will be constant for a given engine. Locate the excessive heat out. Once the excessive heat out is located you will be able to identify a potential solution.
The dash gauge may not be accurate. Further troubleshooting is required. Complete the following checklist when you are diagnosing a complaint of overcooling .
- Describe the complaint:
Vehicle make and model
Engine Serial number
Mileage on the engine and vehicle
Dealer Code
Summarize the complaint for overcooling:
Does the engine run cold at idle?____(Y/N)
Does the engine run warm at idle but the coolant temperature drops below 80 °C (175 °F) when driving the truck unloaded?____(Y/N)
Does the truck run cold when the truck is loaded?____(Y/N)
Is the cap getting heat?____(Y/N)
Cab Temperature____°C
Other?
List all of the heaters or coolers. (Example: internal tank fuel heaters, bulk heaters, transmissions coolers, extra bunk heaters)
Is the cooling fan on or is the cooling fan cycling when the engine is getting over cooled?________(Y/N on/cycling)
Does the fan operate correctly in the trucks with the complaint? (The fan turns on when the ECM tells the fan to turn on.)____(Y/N)
The version of software on the engine________
- Verify overcooling with the ECM data. The dash gauge may not be accurate. List your results in the following table.
Show/hide table
Table 1     Temperature     ECM OEM Gauge Ambient air Temperature     °C     Jacket water coolant temperature at idling (1100 RPM)     °C     °C     Jacket water coolant temperature with light load     °C     °C     Jacket water coolant temperature with heavy load     °C     °C     - If the dash gauge reads significantly different than the ECM, the dash gauge may need to be repaired.
- If the engine is warm but the cab is not getting heat there might be a problem with the heating in the ducting for the cab.
- If the dash gauge reads significantly different than the ECM, the dash gauge may need to be repaired.
- Leakage from the thermostat
The leakage of the thermostat is measured at the top radiator hose. The thermostats are rated at a maximum of 10 cc a minute per thermostat.
- Check valve for the Vent line
A check valve for the vent line in overcooling issues has been used in the past. The publication on the check valve for vent line is Truck Engine News, "New Cooling System Vent Line Check Valve Helps Prevent Over Cooling". If this check valve is used on the C15 On-highway engine the check valve must be installed above the tee. The tee connects the vent line for the precooler and the standard vent line together.
- Other heater circuits
Check the routing of all hoses.
Isolate one circuit at a time. If one of the repairs fixes the issue, a closer look will be required. The possible heater circuits may include the following: fuel coolers, lower radiator hoses and heater for fuel tank .