2006 GMC Yukon Owner's Manual - Page 401

{CAUTION: Turning the surge tank pressure cap when the engine and radiator are hot can allow steam and scalding liquids to blow out and burn you badly. Never turn the surge tank pressure cap - even a little - when the engine and radiator are hot. The vehicle must be on a level surface. When your engine is cold, the coolant level should be at the FULL COLD mark. If your vehicle is equipped with a low coolant sensor and the LOW COOLANT LEVEL message comes on and stays on, it means you are low on engine coolant. See "LOW COOLANT LEVEL" under DIC Warnings and Messages on page 3-56. {CAUTION: You can be burned if you spill coolant on hot engine parts. Coolant contains ethylene glycol, and it will burn if the engine parts are hot enough. Do not spill coolant on a hot engine. When replacing the pressure cap, make sure it is hand-tight and fully seated. Coolant Surge Tank 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. The coolant surge tank pressure cap must be fully installed on the coolant surge tank. See Engine Compartment Overview on page 5-12 for more information on location. Adding Coolant If you need more coolant, add the proper DEX-COOL® coolant mixture at the surge tank, but only when the engine is cool. 5-27