The vehicle must be on a level surface when checking the coolant level.
It is normal to see coolant moving in the upper coolant hose return line when the engine is running.
Check to see if coolant is visible in the coolant surge tank. If the coolant inside the coolant surge tank is boiling, do not do anything else until it cools down.

If coolant is visible but the coolant level is not at or above the mark pointed to, add a 50/50 mixture of clean drinkable water and DEX-COOL coolant.
Be sure the cooling system is cool before this is done.
What to Use
How to Add Coolant to the Coolant Surge TankTire Terminology and Definitions
Air Pressure: The amount of air inside the tire pressing outward on each square
inch of the tire. Air pressure is expressed in kPa (kilopascal) or psi (pounds per
square inch).
Accessory Weight: The combined weight of optional accessories. Some examples
of optional accessories are automatic t ...
How Does an Airbag Restrain?
In moderate to severe frontal or near frontal collisions, even belted occupants
can contact the steering wheel or the instrument panel. In moderate to severe side
collisions, even belted occupants can contact the inside of the vehicle.
Airbags supplement the protection provided by safety belts ...
Emergency
With Automatic Crash Response, the OnStar system can automatically connect to
an OnStar Emergency Advisor. The built-in system can automatically connect to help
in certain crashes.
Press to connect to an OnStar Emergency
Advisor. GPS technology is used to identify the vehicle location and ca ...