Pinpoint Test 3: The Engine Does Not Reach Normal Operating Temperature
-
PINPOINT TEST 3: THE ENGINE DOES NOT REACH NORMAL OPERATING TEMPERATURE - HYBRID
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). 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, see - Engine Cooling Description/Operation.
- DTC P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
Possible Causes
- Low coolant level
- Thermostat
- CHT indicator system (gauge)
- Engine cooling fan
Diagnostic Procedure
WARNING: Always allow the engine to cool before opening the cooling system. Do not unscrew the coolant pressure relief cap when the engine is operating or the cooling system is hot. The cooling system is under pressure; steam and hot liquid can come out forcefully when the cap is loosened slightly. Failure to follow these instructions may result in serious personal injury.
