2006 Hummer H2 Owner's Manual - Page 359

Cooling System When you decide it is safe to lift the hood, here is what you will see: If the coolant inside the coolant surge tank is boiling, do not do anything else until it cools down. The vehicle should be parked on a level surface. Check the coolant level after the system cools down. Some amount of coolant may be lost due to overheating. The coolant level should be at or above the FULL COLD mark. If it is not, you may have a leak at the pressure cap or in the radiator hoses, heater hoses, radiator, water pump, or somewhere else in the cooling system. {CAUTION: Heater and radiator hoses, and other engine parts, can be very hot. Do not touch them. If you do, you can be burned. Do not run the engine if there is a leak. If you run the engine, it could lose all coolant. That could cause an engine fire, and you could be burned. Get any leak fixed before you drive the vehicle. A. Coolant Surge Tank B. Coolant Surge Tank Pressure Cap C. Engine Cooling Fan 5-29