Pinpoint Test C: The Engine Does Not Reach Normal Operating Temperature

Normal Operation 

The engine cooling system functions to maintain engine temperatures during operation. Correct coolant flow through the engine, radiator and remainder of cooling system passages and components is essential to maintaining a correct engine temperature.

Engine coolant flows primarily from the engine to the radiator circuit and back to the coolant pump. From the coolant pump, coolant is sent through the engine block and cylinder heads. A separate circuit from the engine also feeds the heater core with coolant. On most engines, the coolant pump is operated by engine rotation through a pulley which is driven by the accessory drive belt to circulate the coolant. Some engines use a belt driven by a pulley attached to the camshaft, and some engines use a sprocket driven by the timing chain to operate the coolant pump. The coolant thermostat is a control valve actuated by coolant temperature. When the thermostat is closed, coolant flow bypasses the radiator circuit and returns to the coolant pump. When the thermostat is opened, coolant is allowed to flow through the radiator circuit in order to transfer engine generated heat to the outside air.

Concerns of engine inability to reach normal operating temperature typically occur when the rate of coolant flow through some coolant circuits (radiator, heater core) is more than expected given the conditions, or when the cooling fans operate all the time (electric fans) or the fan clutch is always engaged (engine driven fans). Heat is not allowed to build in the engine because a heat exchanger is removing too much heat, including the radiator, heater core and oil cooler. In addition, perceived concerns that the engine does not reach normal operating temperature can be related to a low coolant level or trapped air which does not allow for hot coolant to be available at the heater core, an inoperative climate control system, or for concerns perceived or related to an incorrect engine temperature gauge indication.

For vehicle/engine specific information, refer to Engine Cooling 

• DTC P0125 Insufficient Coolant Temp for Closed Loop Fuel Control
• DTC P0128 Coolant Thermostat (Coolant Temp Below Thermostat Regulating Temperature)

This pinpoint test is intended to diagnose the following:

• Low coolant level
• Thermostat
• Engine coolant temperature (ECT) indicator system (gauge)
• Engine cooling fan

PINPOINT TEST C: THE ENGINE DOES NOT REACH NORMAL OPERATING TEMPERATURE 

1. C1 CARRY OUT INSPECTION AND VERIFICATION 
   • Carry out the Inspection & Verification .
   • Were any concerns found? 
   1. YES  : REPAIR as needed. TEST the system for normal operation.
   2. NO  : Go to  C2.
2. C2 CHECK FOR DTCs P0125 or P0128 
   NOTE: Refer to the Introduction - Gasoline Engines article for correct scan tool hook-up procedure.
   • Check for DTC P0125 or P0128.
   • Is DTC P0125 or P0128 present? 
   1. YES  : If the vehicle is equipped with an electric cooling fan, go to  C3. If the vehicle is equipped with only a mechanical cooling fan, go to  C4.
   2. NO  : The cooling system is operational. If an inoperative engine coolant temperature gauge is suspected, CHECK the engine coolant temperature gauge operation. REFER to INSTRUMENTATION, MESSAGE CENTER, & WARNING CHIMES article. If an inoperative climate control system is suspected, CHECK the climate control system operation. REFER to CLIMATE CONTROL SYSTEM - GENERAL INFORMATION & DIAGNOSTICS article. If any other DTCs are retrieved, REFER to the Introduction - Gasoline Engines article.
3. C3 CHECK THE ELECTRIC COOLING FAN OPERATION 
   • Allow the engine to cool.
   • Make sure the A/C switch is OFF (if equipped).
   • Start the engine.
   • Check the electric cooling fan.
   • Is the electric cooling fan on all the time? 
   1. YES  : DIAGNOSE the electric cooling fan operation. REFER to the Introduction - Gasoline Engines article.
   2. NO  : If the vehicle is also equipped with a mechanical cooling fan, go to  C4. Otherwise, go to  C5.
4. C4 CHECK THE MECHANICAL COOLING FAN OPERATION 
   • Carry out the Cooling Fan Clutch Component Test. For a mechanical cooling fan clutch, refer to Component Tests . For an electronic cooling fan clutch, refer to the Introduction - Gasoline Engines article.
   • Is the cooling fan clutch OK? 
   1. YES  : Go to  C5.
   2. NO  : INSTALL a new cooling fan clutch. TEST the system for normal operation.
5. C5 CHECK THE COOLANT LEVEL 
   NOTE: Allow the engine to cool before checking the coolant level.
   • Visually check the engine coolant level in the degas bottle or coolant expansion tank.
   • Is the engine coolant level within specification? 
   1. YES  : INSTALL a new thermostat. TEST the system for normal operation.
   2. NO  : Go to Pinpoint Test A  to diagnose a coolant leak.