2008 GMC Yukon Owner's Manual - Page 398

Checking Coolant {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. The coolant surge tank is located in the engine compartment on the passenger's side of the vehicle. See Engine Compartment Overview on page 5-14 for more information on location. 5-30