Cooling System Description and Operation (L84, L87)

Engine Coolant Indicators Engine Hot - AC Off The instrument panel cluster (IPC) displays Engine Hot - AC Off message when the IPC receives a message from the powertrain control module (PCM) requesting illumination of this driver warning when the temperature reaches 125°C (257°F). Engine Hot - Idle Engine The IPC Engine Hot - Idle Engine when the IPC receives a message from the PCM requesting illumination of this driver warning when the temperature reaches 128°C (262°F). Engine Hot - Turn Engine Off The IPC displays Engine Hot - Turn Engine Off message when the IPC detects a reduced engine power condition from the PCM. The IPC receives a message from the PCM requesting illumination when the engine temperature reaches 135°C (275°F). Coolant Heater (If Equipped) The optional coolant heater (RPO K05) operates using 110 V AC external power and is designed to warm the coolant in the engine block area for improved starting in very cold weather. The coolant heater also helps reduce fuel consumption when a cold engine is warming up. The unit is equipped with a detachable AC power cord. There is an internal thermal switch in the coolant heater cord that prevents operation above −18°C (0°F). A weather shield on the cord is provided to protect the plug when not in use. Cooling System The cooling system’s function is to maintain an efficient engine operating temperature during all engine speeds and operating conditions. The cooling system is designed to remove various amounts of the heat produced by the burning of the air-fuel mixture. When the engine is cold, the coolant does not flow to the radiator until the thermostat opens. This allows the engine to warm quickly. Cooling Cycle Coolant is drawn from the radiator outlet and into the water pump inlet by the water pump. Coolant will then be pumped through the water pump outlet and into the engine block. In the engine block, the coolant circulates through the water jackets surrounding the cylinders, where it absorbs heat. Some coolant is also pumped from the water pump to the heater core, then back to the water pump. This provides the passenger compartment with heat and defrost. The coolant is then forced through the cylinder head gasket openings and into the cylinder heads. In the cylinder heads, the coolant flows through the water jackets surrounding the combustion chambers and valve seats, where it absorbs additional heat. Coolant The engine coolant is a solution made up of a 50-50 mixture of DEX-COOL® and suitable drinking water. The coolant solution carries excess heat away from the engine to the radiator, where the heat is dissipated to the atmosphere. Radiator The radiator is a heat exchanger. It consists of a core and two 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 radiator drain cock, located in the bottom of the right hand tank. The radiator drain cock unit includes the drain cock and drain cock seal. The radiator removes heat from the coolant passing through it. The fins on the core transfer heat from the coolant passing through the tubes. As air passes between the fins, it absorbs heat and cools the coolant. Auxiliary Coolant Pump An auxiliary coolant pump is used to circulate coolant through the cabin heater cores during Stop/Start operation to improve cabin heating performance. Radiator Surge Tank and Radiator Surge Tank Cap The radiator surge tank is a plastic tank with a threaded pressure radiator surge tank cap that contains a blow off or pressure relief valve, vacuum or atmospheric valve and seals the cooling system. The radiator surge tank is mounted at a point higher than all other coolant passages. The radiator surge tank provides an air space in the cooling system that allows the coolant to expand and contract. The radiator surge tank provides a coolant fill point and a central air bleed location. The radiator surge tank cap pressure valve is held against its seat by a spring, which protects the radiator from excessive cooling system pressure. 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. During vehicle use, the coolant heats and expands. The pressure cap allows cooling system pressure to build up as the temperature increases. As the pressure builds, the boiling point of the coolant increases. Engine coolant can be safely run at a temperature much higher than the boiling point of the coolant at atmospheric pressure. The hotter the coolant is, the faster the heat transfers from the radiator to the cooler, passing air. Increased coolant volume flows into the radiator surge tank. If the pressure in the cooling system exceeds the rating of the pressure cap, it raises the pressure valve, venting the excess pressure through a channel into the overflow bottle. As the coolant circulates, the air is allowed to bubble out. This air is then transferred to the overflow bottle, through the radiator surge tank cap, where it returns to the atmosphere. Coolant without air bubbles absorbs heat much better than coolant with bubbles. When the engine cools, the coolant, without air bubbles, contracts back into the radiator surge tank from the bottom of the overflow bottle and a vacuum is created in the cooling system. This vacuum causes the vacuum valve to open, allowing outside air into the radiator surge tank. This equalizes the pressure in the cooling system with atmospheric pressure, preventing the radiator and coolant hoses from collapsing. Air Baffles and Seals The cooling system uses deflectors, air baffles 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 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 Oil Cooler Excessive heat in the engine oil is removed via a heat exchanger located in the right side tank of the radiator. The engine oil temperature is controlled by the temperature of the engine coolant that surrounds the oil cooler in the radiator. The engine oil pump, pumps the oil through the engine oil cooler line to the oil cooler. The oil then flows through the cooler where excessive heat is transferred to the engine coolant. The oil is then pumped through the oil cooler return line, to the engine block system. Transmission Oil Cooler Excessive heat in the transmission oil is removed via a heat exchanger located in front of the air conditioning condenser. The transmission oil temperature is controlled by the ambient air flowing by the cooler. The transmission oil pump, pumps the oil through the transmission oil cooler line to the oil cooler. The oil then flows through the cooler where excessive heat is transferred to the ambient air. The oil is then pumped through the oil cooler return line, to transmission. Flow to the cooler only occurs when the oil temperature is above the setting of the Thermal By- Pass valve.