1999 GMC Sonoma Owner's Manual - Page 215

yellowblue Cooling System When you decide it's safe to lift the hood, here's what you'll see: If the coolant inside the coolant recovery tank is boiling, don't do anything else until it cools down. A. Coolant Recovery Tank B. Radiator Pressure Cap C. Engine Fan The coolant level should be at least up to the ADD mark. If it isn't, you may have a leak in the radiator hoses, heater hoses, radiator, water pump or somewhere else in the cooling system. 5-11