2005 GMC Canyon Owner's Manual - Page 305

How to Add Coolant to the Radiator 4. Then fill the coolant recovery tank to the FULL COLD mark. 1. You can remove the radiator pressure cap when the cooling system, including the upper radiator hose, is no longer hot. Turn the pressure cap slowly counterclockwise about one full turn. If you hear a hiss, wait for that to stop. A hiss means there is still some pressure left. 2. Then keep turning the cap to remove it. 3. Fill the radiator with the proper DEX-COOL® coolant mixture, up to the base of the filler neck. See Engine Coolant on page 5-25 for more information about the proper coolant mixture. 5-33 5. Reinstall the cap on the coolant recovery tank, but leave the radiator pressure cap off.