Normal Operation

WARNING: This page is about a different variant/trim than selected.

The engine cooling system maintains 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. The 2.5L engine coolant pump is operated by engine rotation through a pulley driven by the accessory drive belt. The 3.0L coolant pump is operated by a V-ribbed belt driven by a pulley attached to the camshaft. The 3.5L coolant pump is operated through a sprocket driven by the timing chain. 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, or when the electric cooling fans operate all the time. 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 engine specific information, refer to ENGINE COOLING in the Description and Operation portion of this section.

DTC P0125 (Insufficient Coolant Temp for Closed Loop Fuel Control) - Indicates the Cylinder Head Temperature (CHT) sensor has not achieved the required temperature level to enter closed loop operating conditions within a specified amount of time after starting the engine.
DTC P0128 (Coolant Thermostat [Coolant Temp Below Thermostat Regulating Temperature]) - Indicates that the thermostat monitor has not achieved the required engine operating temperature within a specified amount of time after starting the engine.

This pinpoint test is intended to diagnose the following:

Low coolant level
Thermostat
Engine Coolant Temperature (ECT) gauge
Engine cooling fan