PINPOINT TEST C : The Engine Does Not Reach Normal Operating Temperature: Notes

Normal operation and Fault Conditions 

The engine cooling system maintains engine temperature 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. Coolant is sent from the coolant pump through the engine block and cylinder heads. A separate circuit from the engine also feeds the heater core with coolant. The coolant pump circulates the coolant. 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 flows 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. 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.

The engine cooling system incorporates a coolant bypass solenoid valve and a coolant shutoff solenoid valve. Using these two valves, the coolant flow through the engine block can be restricted or completely stagnated. The restriction or stagnation of the coolant flow makes it possible for the engine components to warm up faster during the warm-up phase. The coolant shutoff solenoid valve is normally open and closes when energized to stagnate coolant flow throughout the cooling system if the coolant bypass solenoid valve is closed. The coolant shutoff solenoid valve blocks or allows coolant flow through the thermostat housing, coolant pump, engine block, heater core, turbocharger, transmission oil cooler, and engine oil cooler. The coolant bypass solenoid valve provides another coolant circuit for the engine block and is normally closed and opens when energized to provide coolant flow between the outlet of the engine block to the thermostat housing. The primary function of this valve is to increase coolant flow through the engine block reducing cooling system pressure and temperature fluctuations during high engine loads. The coolant bypass solenoid valve is commanded open during high engine temperatures to provide more cooling. If the coolant bypass solenoid valve mechanically sticks open the engine takes longer to reach operating temperature.

Possible Sources 

• Low coolant level
• Thermostat
• Coolant bypass solenoid valve
• ECT sensor
• Temperature gauge

Diagnostic Trouble Code (DTC) Fault Trigger Conditions