The cooling system maintains engine temperature at an efficient level during all engine operating conditions. The cooling system consists of the following components:

A thermostat controls coolant circulation. The thermostat remains closed until the engine reaches normal operating temperature. When the engine is cold, coolant does not circulate through the radiator. This allows for faster engine warm-up. When the engine reaches normal operating temperature, the thermostat opens, and the coolant circulates through the radiator in order to keep the engine from overheating.

The L36 and L67 engines have a closed cooling system. This means you can add coolant to the coolant recovery reservoir without removing the pressure cap from the radiator.

On the L47 engine, remove the surge tank pressure cap in order to add coolant.

The 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.

In the 4.0L cooling system, the coolant pump takes coolant from the radiator and passes the coolant through the thermostat on the inlet side of the pump. The coolant enters the block at the rear of the engine from the crossover. The coolant is then routed through the cylinder heads back to the crossover. At this point the coolant has the following 4 possible routes:

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 Sequential Fuel Injection (SFI) system has coolant passages in the throttle body. The coolant flow improves cold driveability.

This sensor monitors the coolant level in the cooling system and indicates if the coolant is low. This sensor is at the base of the radiator surge tank.

This probe monitors the coolant level in the cooling system and indicates if the coolant level is low.

The probe is mounted on the right side radiator end tank. Remove the probe by uncoupling and pulling the probe from the radiator end tank.

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 and increase radiator cooling.

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.