The cooling systems function is to maintain an efficient engine operating temperature during all engine speeds and operating conditions. The cooling system is designed to remove approximately one-third 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.

Coolant is drawn from the radiator outlet to the thermostat. The flow of coolant will be stopped at the thermostat until the engine is warmed; while the thermostat is closed the water pump circulates coolant through the engine block and heater core. An electric auxiliary water pump is used on the heater core outlet circuit to aid in flow through the heater loop with KL9. This auxiliary water pump is enabled when the heater control is set to request heat, and the vehicle is in the STOP mode of the AUTOSTOP feature. Coolant is returned to the water pump through the engine bypass and the heater core outlet hose. This provides the passenger compartment with heat and defrost.

After the thermostat opens, the coolant is pumped through the water pump outlet and into the engine block and heater core. In the engine block, the coolant circulates through the water jackets surrounding the cylinders where it absorbs heat.

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.

From the cylinder heads, the coolant is then forced into the radiator where it is cooled and the coolant cycle is completed.

Operation of the cooling system requires proper functioning of all cooling system components. The cooling system consists of the following components:

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.

The engine water outlet includes a engine coolant bypass valve, which opens at around 4,000 RPM. All coolant is circulated through the heater core when the RPM is below 4,000 while the engine thermostat is fully closed during engine warm up. The engine coolant bypass valve opens at around 4,000 RPM and above, which stops increase of flow rate to the heater core and forces some portion of coolant through a heater bypass loop in order to protect the heater core from excessive coolant pressure. In rare cases, the engine coolant bypass valve may be stuck open, causing a lack of cabin heat.

The radiator is a heat exchanger consisting of a core and 2 tanks. The aluminum core is a tube and fin cross-flow 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 right hand tank. The 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.

The thermostat controls the flow of coolant and is mounted to the cylinder head. The thermostat contains a wax pellet that expands and contracts based on the coolant temperature, which will mechanically move the main spring and a sealing disc to control the flow of coolant.

The surge tank is a plastic tank with a threaded pressure cap. The tank is mounted at a point higher than all other coolant passages. The surge tank provides an air space in the cooling system that allows the coolant to expand and contract. The surge tank provides a coolant fill point and a central air bleed location. During vehicle use, the coolant heats and expands. The increased coolant volume flows into the surge tank. As the coolant circulates, any air is allowed to bubble out. Coolant without air bubbles absorbs heat much better than coolant with bubbles.

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 A/C condenser, and prevent recirculation of hot air for better hot weather cooling and A/C condenser performance.

The transmission oil cooler is an air-to-oil heat exchanger integrated with the A/C condenser, occupying the top seven rows. Transmission fluid is supplied to the cooler inlet, where it passes through a series of tubes and is returned to the transmission sump. Transmission fluid temperature is regulated by air passing through the cooler fins, between the tubes, carrying away heat to the atmosphere.

A temperature/pressure fluid bypass valve is mounted to the end of the cooler. By design, transmission fluid bypasses the cooler to provide quick transmission warm-up where efficient shift schedules can be achieved. As the transmission fluid achieves proper operating temperature, the thermostatic bypass valve closes, and fluid is routed through the cooler to manage fluid temperature. When a pressure drop (due to cooler blockage) is present, the bypass valve will open to bypass the cooler, returning the fluid to the transmission sump.