System Operation
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 and turbocharger with coolant. The coolant pump, operated by engine rotation through the accessory drive belt, 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 to transfer engine-generated heat to the outside air.
The transmission cooler - warmer is mounted on the transmission. On initial startup, the transmission fluid heater coolant control valve opens and allows warm coolant from the engine to enter the transmission cooler - warmer to warm the transmission fluid. As the engine and transmission warm, the transmission fluid heater coolant control valve closes and the transmission fluid cooler coolant control valve opens, allowing cooler coolant from the radiator to enter the transmission cooler - warmer to cool the transmission fluid.
The degas bottle holds surplus coolant and removes air from the cooling system. It also allows for coolant expansion and system pressurization, replenishes coolant to the cooling system and serves as the location for service fill.
The thermostat monitor is a function of the PCM and is designed to verify correct thermostat operation. The monitor executes once per drive cycle and has a monitor run duration of 300-800 seconds. If a malfunction occurs, DTC P0125 or P0128 sets, and the MIL illuminates.
The engine's cooling circuit consists of an additional coolant bypass solenoid valve and coolant shutoff solenoid valve. Using these two valves, the coolant flow through the engine is specifically restricted or stagnated in the warm-up phase. This restriction of the coolant flow makes it possible for the engine components to warm up faster. The result is a significant reduction in the emissions of harmful pollutants and an improvement in fuel economy (i.e. reduced friction) during the warm-up phase. Both solenoid valves are controlled by the PCM .
The following input parameters are used to do this
- Coolant temperature
- Ambient air temperature
- Engine speed
- Engine load
- Status of the air conditioning system
Warm-up regulation is performed in four phases. Phase 1 or 2 occurs after initial engine start-up depending on the ambient air temperature.
Phase 1
During an initial engine start-up with an ambient temperature is 60-75°F (16-24°C) or warmer (calibratable) the coolant shutoff solenoid valve closes and the coolant bypass solenoid valve remains closed. With both valves closed the coolant is stagnant and does not circulate in the engine (cylinder block and cylinder head) or through any other cooling system component to significantly decrease the engine warm up time. This reduces emissions and fuel consumption during warm-up.
Phase 2
During an initial start-up with an ambient temperature 60-75°F (16-24°C) or cooler (calibratable) the coolant shutoff solenoid valve remains open. This allows engine coolant to circulate through the heater core providing cabin heat to the customer. When the coolant shutoff solenoid valve is open, the coolant circulates through the engine (cylinder block and cylinder head), heater core, engine oil cooler, transmission oil cooler, turbo, and degas bottle. Coolant is also routed into the thermostat housing which initiates the warm-up phase of the thermostat.
Phase 3
The coolant bypass solenoid valve is energized and opens when engine coolant reaches (158°F) 70°C and the engine load is greater than 70% or engine speed is greater than 4, 000rpm. When the coolant bypass solenoid valve opens coolant is routed through a coolant between the engine block output and thermostat housing. The opening of this coolant circuit increases the coolant flow rate through the engine block which reduces cooling system pressure and temperature fluctuations in the engine block.
Phase 4
At about (180°F) 82°C, the thermostat opens and the coolant is routed through the radiator. However, the thermostat opening temperature is partially variable via the coolant bypass solenoid valve. The temperature around the thermostat and its expansion element is the total of the coolant temperatures entering the thermostat housing. Targeted actuation of the coolant bypass solenoid valve allows increased flow of coolant from the engine block to contact the thermostat element and allows an actual coolant temperature of between (180°F) 82°C and (198°F) 92°C to be set. During part throttle driving, fuel consumption depends heavily on coolant temperature. Closing of the coolant bypass solenoid valve makes it possible to drive with a higher coolant temperature during part throttle conditions.
Normal operation and Fault Conditions
The engine cooling system is a closed system providing for coolant expansion and contraction as well as changes in pressure as coolant warms and cools with engine operation. Various gaskets, seals, hoses and clamps contain coolant within the cooling system and keep other fluids and contaminants from entering the cooling system. Coolant loss can be attributed to either external or internal leaks anywhere within the cooling system.
The engine cooling system maintains the 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 to transfer engine-generated heat to the outside air.
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 also 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. If one or both valves do not open when commanded by the PCM an engine over temperature condition can result.
Engine overheating generally occurs when there is a disruption in the ability to control either coolant flow at the correct rate, the inability to transfer heat from the engine through the coolant (including low coolant) or an inability to transfer engine-generated heat to the outside air through the radiator.
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.
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. Both solenoid valves are controlled by the PCM via a low side driver. The PCM monitors both solenoids for electrical faults and sets an appropriate DTC .
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. Both solenoid valves are controlled by the PCM via a low side driver. The PCM monitors both solenoids for electrical faults and sets an appropriate DTC .