1994 GMC Yukon Owner's Manual - Page 142

Heater Output Engine Coolant Heater If your vehicle has a diesel engine, it is equipped with an engine coolant heater. An engine coolant heater is optionalon gas engine vehicles. You can use an engine coolantheater during initial start-up in cold weather (20" F, -8" C, or lower) to help heat thepassenger compartment faster. Because an engine coolantheater warms the engine coolant, your vehicle's heating system can provide some heat as soon as you start the engine. The use of anengine coolantheater also reduces the time it takes for the engine to reach normal operating temperature, and shortens the time it takes the heater to reach full output. For more information, See"Engine Coolant Heater" in the Index. Diesel Engine If you idle your diesel engine for a long time when it's cold outside, your heater may blow out cool air. This isnormal. When you increase the engine speed, your heater should blow out warmer air. If it doesn't, your coolant level may be low. See "EngineCoolant" in the Index to find out how to check your coolant level. Heating System (Without Air Conditioning) If your vehicle does not have air conditioning, this is what yourheating system will look like. 3-4