2010 GMC Canyon Extended Cab Owner's Manual - Page 310

7. By this time, the coolant level inside the radiator filler neck might be lower. If the level is lower, add more of the proper DEX-COOL® coolant mixture through the filler neck until the level reaches the base of the filler neck. 8. Then replace the pressure cap. At any time during this procedure if coolant begins to flow out of the filler neck, reinstall the pressure cap. Notice: If the pressure cap is not tightly installed, coolant loss and possible engine damage may occur. Be sure the cap is properly and tightly secured. 6. Start the engine and let it run until you can feel the upper radiator hose getting hot. Watch out for the engine cooling fan. 6-34