The cooling system maintains proper engine temperature at an efficient level under all operating conditions. When the engine is cold, coolant in the radiator does not circulate, allowing for faster engine warm-up.

The thermostat remains closed until the engine reaches the proper operating temperature. Once the engine reaches normal operating temperature, the thermostat opens, and the coolant circulates through the crossflow radiator in order to keep the engine from overheating.

The cooling system includes the following components:

In the Northstar cooling system, the coolant pump takes coolant from the radiator and passes the coolant through the thermostat on the inlet side of the coolant pump. The coolant enters the block at the rear of the engine from the water crossover, then the coolant is routed through the cylinder heads back to the water crossover. At this point the coolant has four 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 throttle body coolant system uses pipes and hoses to divert coolant to the throttle body. Coolant flows through the throttle body for cold weather starts and helps provide a smooth idle until the engine reaches operating temperature.

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.

The surge tank uses a pressure-vent cap to allow a buildup of 103 kPa (15 psi) in the cooling system. The cap allows the system to operate at a higher-than-atmospheric pressure. This pressure raises the boiling point of the coolant to about 125°C (262°F) at sea level.

The pressure-type cap contains a blowoff (pressure) valve (2) and a vacuum (atmospheric) valve (1). The cap protects the radiator by relieving any pressure that exceeds 103 kPa (15 psi).

In order to prevent radiator collapse, caused by vacuum as the engine cools, the vacuum valve prevents excessive pressure differences from occurring between the cooling system and the atmosphere.

The surge tank cap has a new threaded design to allow for easier and safer removal. In order to safely remove the cap from a cool system, do the following steps:

Caution: With a pressurized cooling system, the coolant temperature in the radiator can be considerably higher than the boiling point of the solution at atmospheric pressure. Removal of the surge tank cap, while the cooling system is hot and under high pressure, causes the solution to boil instantaneously with explosive force. This will cause the solution to spew out over the engine, the fenders, and the person removing the cap. Serious bodily injury may result.

1. Slowly rotate the cap counterclockwise ¼ turn and then stop, do not press down.
2. Allow any residual pressure, indicated by a hissing sound, to be relieved.
3. After the hissing stops, continue to rotate the cap counterclockwise until the cap is removed.

There is no specific orientation of the lettering on the cap versus the cap being tight. To retighten the cap, use hand tight pressure.