This vehicle has a pressure-type engine cooling system. A thermostat controls the coolant circulation.

The cooling system consists of the following components:

A 103 kPa (15 psi) radiator or surge tank cap seals the cooling system, causing the system to operate at a higher than atmospheric pressure. The high pressure operation raises the boiling point of the coolant to about 125 ° C (257 ° F), increasing the cooling efficiency of the radiator.

The pressure-vacuum valve radiator cap, used with gasoline engines, allows the coolant to expand through the pressure valve in the center of the cap without building up unnecessary pressure. The expanding coolant flows into the coolant recovery reservoir and the vent valve closes because of coolant expansion and flow. Any air in the system is forced into the coolant recovery reservoir and then out of the vent tube at the top of the reservoir. As the system cools, vacuum forces the coolant in the reservoir back to the radiator through the vent valve. Because of this, the radiator remains full at all times.

The diesel engine uses a cooling system with a surge tank. The pressure cap for the diesel engine differs from the gasoline engine pressure cap. The cap is on the surge tank. The diesel engine uses a pressurized surge tank. Coolant circulates through the surge tank. The surge tank allows the escape of any air in the system and provides room for coolant expansion when the coolant is hot.

The cooling system reaches 103 kPa (15 psi) in either system only after the system reaches normal operating temperature.

This vehicle has a newly developed engine coolant. GM Goodwrench DEX-COOL™ was developed to last for 166 000 km (100,000 mi) or 5 years, whichever occurs first. Follow the instructions in Draining/Filling Cooling System. Make sure only GM Goodwrench DEX-COOL™ (orange-colored, silicate-free) is used when coolant is added or changed.

A 50/50 mixture of ethylene glycol (GM Goodwrench DEX-COOL™) and water will provide the following protection:

Notice: Pure coolant can be added to raise the boiling point of the coolant, but too much will affect the freezing point. Do not use a solution stronger than 70 percent, as the freeze level rises rapidly after this point. Pure coolant will freeze at -22°C (-8°F).

The fan and the clutch mount to the water pump. The clutch has a heat sensitive spring that contracts as the engine temperature changes. This factor determines how fast the fan blades turn in order to cool the radiator.

This switch activates a warning lamp in the Instrument Panel Cluster if the engine overheats. With optional instrumentation, a temperature gauge replaces the warning lamp and a transducer replaces the temperature switch. For location and diagnosis of the switch, refer to Temperature Lamp Switch in Electrical Diagnosis.

A deflector redirects air flow. Deflectors are installed under the vehicle and redirects the air flow beneath the vehicle to flow through the cooling system. The deflectors perform the following functions:

Air baffles are used to direct air into the radiator and A/C condenser. Air seals ensure that air passes through, and does not bypass, the radiator and the A/C condenser. A missing, damaged, or incorrectly installed baffle or seal may cause the engine to overheat.

The front engine-mounted coolant pump is belt driven. Coolant from the radiator outlet flows to the coolant pump inlet, and the coolant is pumped through coolant passages in the crankcase and into the cavities surrounding the cylinders. Coolant then flows through holes in the cylinder head gaskets into the cylinder head coolant passages.

Passages in the intake manifold direct the coolant to the thermostat. When the thermostat is closed, the coolant is prevented from returning to the radiator, and the coolant is recirculated for quick engine warm-up.

When the engine reaches operating temperature, the thermostat opens, and the coolant flows to the inlet tank on the top left side of the radiator. The coolant is cooled as the coolant flows across the horizontal core tubes to the outlet tank on the right side of the radiator. This completes the coolant flow cycle.

Problems not requiring disassembly of the cooling system:

Problems requiring disassembly of the cooling system: