2004 Chevrolet Silverado 1500 Pickup Owner's Manual - Page 425

If you have to add coolant more than four times a year, have your dealer check your cooling system. Notice: If you use the proper coolant, you do not have to add extra inhibitors or additives which claim to improve the system. These can be harmful. {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're low on engine coolant. See "Low Coolant Level" under DIC Warnings and Messages on page 3-65. Checking Coolant The coolant surge tank is located in the engine compartment on the passenger's side of the vehicle. See Engine Compartment Overview on page 5-12 for more information on location. 5-33