Cooling System

This vehicle uses an improved cooling system design, which makes use of an Active Thermal Management (ATM) strategy. The difference between conventional cooling systems that use mechanical water pumps and active thermal management is that the predominant goal of the ATM strategy is to prioritize fuel economy by maintaining an ideal engine operating temperature during all engine speeds and operating conditions, while still meeting customer expectations for vehicle performance and reducing vehicle emissions.

The key features of ATM include:

• Engine: Internal
  • Integrated manifold that pulls heat from the engine exhaust.
  • Improved engine coolant jacket that targets hot spots in the engine.
• Engine Mounted
  • Electric water pump that replaces the conventional mechanical water pump.
  • One valve that contains two coolant control valves, called the engine coolant flow control valve and the block control valve, that both eliminate the need for the conventional cooling system thermostat.
  • Engine oil cooler that uses coolant to heat or cool the engine oil as required.
• Transmission Mounted
  • Automatic transmission fluid cooling exchanger that uses coolant to heat or cool the transmission oil as required.
• The Engine control module, which controls the complete ATM system using feedback from numerous sensors.
• Temperature and Position Sensors
  • Engine Block Coolant Temperature Sensor
  • Engine Cylinder Head Coolant Temperature Sensor
  • Engine Inlet Coolant Temperature Sensor
  • Engine Outlet Coolant Temperature Sensor
  • Engine Oil Temperature Sensor 1 and 2
  • Transmission Oil Temperature Sensor
  • Radiator Outlet Coolant Temperature Sensor
  • Heater Core Inlet Coolant Temperature Sensor
  • Heater Core Outlet Coolant Temperature Sensor
  • Control Valve Sensors
• Integrated Manifold
  • The integrated manifold is attached to the side of the engine and is used to extract heat from the exhaust, which can then be directed to either the engine, engine oil cooler, automatic transmission fluid cooling exchanger, or the passenger compartment heater core. The integrated manifold provides a large portion of recuperated heat to the coolant.
• Electric Water Pump
  • The electric water pump is attached to the side of the engine and controls the coolant flow through the entire coolant system. The electric water pump replaces the conventional belt or chain driven pump whose speed is directly coupled to the engine speed. The coolant flow from the electric water pump is not related to engine speed but it is independently controlled by the engine control module.
• Engine Coolant Flow Control Valve
  • The engine coolant flow control valve is attached to the side of the engine, under the integrated manifold. It controls the direction of coolant flow through radiator, bypass, oil heating and oil cooling with one actuator and also eliminates the need for a conventional wax-operated thermostat. It is also controlled by the engine control module through sensor feedback.
• Engine Coolant Flow Control Valve (Block)
  • The block control valve is part of the engine coolant flow control valve and is located on the side of the valve. The block control valve has its own actuator and allows independent/separate control of the block temperature and can be activated at any point during vehicle operation. The combination of the engine coolant flow control valve and the block control valve is critical to achieving optimal combustion chamber temperatures as quickly as possible during engine warm up. This independent control is known as split cooling.
• Engine Oil Cooler
  • The engine oil cooler is a heat exchanger and is attached to the side of the engine and exchanges heat between the engine oil and engine coolant. The engine oil cooler can flow no coolant, provide hot coolant for engine oil heating (during engine warm-up) or provide cooled coolant for engine oil cooling (under high thermal loads).
• Automatic Transmission Fluid Cooling Exchanger
  • The automatic transmission fluid cooling exchanger is a heat exchanger that is attached to the front of the transmission and exchanges heat between the transmission oil and engine coolant. The automatic transmission fluid cooling exchanger can flow no coolant, provide hot coolant for transmission oil heating (during engine warm-up) or provide cooled coolant for transmission oil cooling (under high thermal loads).
• Temperature and Position Sensors
  • Various temperature and position sensors provide data back to the engine control module.
• ATM still uses many of the conventional cooling system features, including:
  • Coolant
  • Coolant Hoses
  • Radiator
  • Radiator Bypass Route
  • Radiator Surge Tank
  • Surge Tank Pressure Cap
  • Engine Coolant Indicators
  • Air Baffles/Guides and Seals
  • Cabin Heater Core Route, if equipped with Rear Cabin Heater

Coolant 

The engine coolant is a solution made up of a 50-50 mixture of DEX-COOL® and suitable drinking water. The coolant solution transfers heat between the components of the engine heating/cooling system.

Radiator 

The radiator is a heat exchanger. It consists of a core and two end tanks. The aluminum core is a tube and fin crossflow design that extends from the inlet tank to the outlet tank. Fins are placed around the outside of the tubes to improve heat transfer to the atmosphere. The inlet and outlet tanks are a molded high temperature nylon reinforced plastic material. A high temperature rubber gasket seals the tank flange edge to the aluminum core. The tanks are clamped to the core with clinch tabs. The tabs are part of the aluminum header at each end of the core.

The radiator also has a drain cock located in the bottom of the left or right hand tank. The drain cock unit includes the drain cock and drain cock seal. Heat is removed from the coolant as the coolant passes through the radiator. The fins on the core transfer heat from the coolant passing through the tubes. Air passing between the fins absorbs the heat and cools the coolant.

Radiator Surge Tank 

The radiator surge tank is a plastic tank with a pressure cap mounted to it. The tank is mounted at a point higher than all other coolant passages. The surge tank provides an air space in the cooling system. The air space allows the coolant to expand and contract. The surge tank also provides a coolant fill point and a central air bleed location. During vehicle use, the coolant heats and expands. The coolant that is displaced by this expansion flows into the surge tank. As the coolant circulates, air is allowed to exit. This is an advantage to the cooling system. Coolant without air bubbles absorbs heat much better than coolant with air bubbles.

Radiator Surge Tank Cap

• The radiator surge tank cap is a pressure cap that seals and pressurizes the cooling system. It contains a blow off or pressure valve and a vacuum or atmospheric valve.
  • The pressure valve is held against its seat by a spring and protects the radiator by relieving pressure if it exceeds 20 psi.
  • The vacuum valve is held against its seat by a spring, which permits opening of the valve to relieve vacuum created in the cooling system as it cools off. The vacuum, if not relieved, could cause the radiator hoses to collapse.
• The pressure cap allows pressure in the cooling system to build up. As the pressure builds, the boiling point of the coolant goes up as well. Therefore, the coolant can be safely run at a temperature higher than the boiling point of the coolant at atmospheric pressure. The hotter the coolant is, the faster the heat moves from the radiator to the cooler passing air. However, if the pressure exceeds the strength of the spring, the pressure valve rises so that the excess pressure can escape. When the engine cools down, the temperature of the coolant drops and a vacuum is created in the cooling system. This vacuum causes the vacuum valve to open, allowing outside air into the cooling system. This equalizes the pressure in the cooling system with atmospheric pressure, thus preventing the radiator hoses from collapsing.

Air Baffles/Guides and Seals 

The cooling system uses deflectors, air baffles/guides and air seals to increase cooling system capability. Deflectors are installed under the vehicle to redirect airflow beneath the vehicle and through the radiator to increase engine cooling. Air baffles/guides are also used to direct airflow through the radiator and increase cooling capability. Air seals prevent air from bypassing the radiator and air conditioning condenser, and prevent recirculation of hot air for better hot weather cooling and air conditioning condenser performance.

Engine Coolant Indicators 

The instrument panel cluster (IPC) shows the engine temperature on the temperature gauge. The value is sent on the data communication line from engine control module. When the coolant temperature is more than 128°C (262°F), the IPC receives a discrete input from engine control module requesting illumination.

The IPC performs the display test at the start of each ignition cycle. The IPC illuminates the TEMP indicator.

Cooling Cycle 

Coolant flows from the electric water pump outlet and into the engine circuit and turbocharger cooling circuit. It also provides cooled coolant flow from the radiator to the engine coolant flow control valve to be used as necessary to manage transmission and engine oil temperature. In the engine, the coolant flow is controlled by the engine coolant flow control valve and the block control valve to provide necessary flow for optimal engine block, cylinder head, and exhaust manifold cooling. The engine coolant flow control valve can also provide the transmission and engine oil circuits warmed coolant from the engine to optimize the oil temperatures. Excess heat is removed from the coolant in the radiator and the cooled coolant returns to the electric water pump.

There are 7 modes of operation in Active Thermal Management, they are as follows:

• Mode 1 (LOW FLOW):
• If the engine is started cold, the system will go to low flow mode, which means the electric water pump runs just enough for the sensors to provide reliable information on the state of the system. The engine heats, the heat stays around the combustion chamber and is not taken away by coolant flow. Low flow mode is the fastest method for engine warm up.

• Mode 2 (ENGINE WARM UP WITH CABIN HEATING ONLY):

  When the driver requests passenger compartment heat or windshield defrosting, the electric water pump will control flow to maximize coolant heat transfer from engine to passenger compartment. This heater circuit is fed by a combination of warmed coolant from the cylinder head, integrated manifold and turbocharger cooler. The engine coolant flow control valve is at an all-closed position at this time. The warmed coolant goes directly to the passenger compartment heater core. Heater core flow returns to the electric water pump.

• Mode 3 (ENGINE WARM UP WITH CABIN HEATING AND RADIATOR BYPASS):

  The cylinder head, integrated manifold and turbocharger cooler passages are still flowing and providing warmed coolant directly to the passenger compartment heater core, if requested. During Mode 2, coolant does not flow through the cylinder head. As combustion chamber temperatures get hotter, it is necessary to flow coolant through the cylinder head without losing heat to the radiator or engine/transmission oil heat exchangers. The engine coolant flow control valve will allow flow through the cylinder head by opening the radiator bypass loop, which returns coolant directly to the electric water pump.

• Mode 4 (ENGINE WARM UP WITH CABIN HEATING, RADIATOR BYPASS AND OIL HEATING):

  The cylinder head, integrated manifold and turbocharger cooler passages are still flowing and providing warmed coolant directly to the passenger compartment heater core, if requested. Once the optimal combustion chamber temperature has been reached, warmed coolant can be used to quickly raise the engine and transmission to their optimal temperatures. The engine coolant flow control valve will still allow flow through the cylinder head with the open radiator bypass loop but will now also allow coolant flow to the engine/transmission oil heat exchangers. Coolant flow from the bypass and heat exchangers returns to the electric water pump.

• Mode 5 (ENGINE-DEMAND COOLING WITH CABIN HEATING AND OIL HEATING):

  The cylinder head, integrated manifold and turbocharger cooler passages are still flowing and providing warmed coolant directly to the passenger compartment heater core, if requested. At this point, the combustion chamber temperature has reached its optimal temperature and the engine needs to dissipate heat through the radiator. Based on engine temperature, the engine coolant flow control valve will split the flow between the radiator and bypass in a ratio necessary to maintain optimal engine temperatures. Additionally, coolant flow will continue to flow to the engine/transmission oil heat exchangers. Engine oil and transmission oil can take significantly longer time to reach optimal temperatures after the engine is already warmed. Coolant flow from the radiator, bypass, and heat exchangers returns to the electric water pump.

• Mode 6 (ENGINE-DEMAND COOLING WITH CABIN HEATING AND OIL COOLING):

  The cylinder head, integrated manifold and turbocharger cooler passages are still flowing and providing warmed coolant directly to the passenger compartment heater core, if requested. On rides in extreme hot driving conditions, the engine and transmission become extremely hot and their oils need to be cooled. The engine coolant flow control valve will continue to split the flow between the radiator and bypass in a ratio necessary to maintain optimal engine temperatures and will now allow colder coolant directly from the electric water pump to flow to the engine/transmission oil heat exchangers. Coolant flow from the radiator, bypass, and heat exchangers returns to the electric water pump.

• Mode 7 (AFTER RUN COOLING):

  The after run mode is after key off and is needed only after extreme hot conditions with high engine, oil and coolant temperatures. For after run mode, the same valve positions are used as in Mode 6, but the electric water pump is run at a lower speed to continue cooling.

• SHUT DOWN

  At engine shutdown, the control valves remain open to permit radiator flow and allow coolant service fill by gravity alone. Both control valves also undergo an integrity check after engine shutdown, which is sometimes audible.