1994 GMC Suburban Owner's Manual - Page 217

If the coolant inside coolant recovery tank is boiling,don't do anything the else until it cools down. The coolant level should be at orabove the COLD 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. 1 NOTICE: Engine damage from running your engine without coolant isn't covered by your warranty. If there seems to be no leak, startthe engine again. Seeif the fan speed increases when idle speed is doubled by pushing the accelerator pedal down. If it doesn't, your vehicle needs service. Turn off the engine. 5-13