1999 GMC Sierra 1500 Pickup Owner's Manual - Page 165

Heater Output Optional Engine Block Heater Ifyourengine is equippedwithanoptionalengineblockheater,youcanuse it during initial start-up in cold weather(20"F, -8"C, orlower) to helpheatthe passengercompartmentfaster.Becauseanengineblockheaterwarmsthe enginecoolant,yourvehicle'sheatingsystemcanprovidesomeheatassoon asyoustarttheengine. it takesforthe Theuse of anengineblockheateralsoreducesthetime engine to reachnormaloperatingtemperature,andshortensthetime it takes theheater to reach full output. Formoreinformation,See"EngineBlock Heater" in theIndex. Diesel Engine If youidleyourdieselengineforalongtimewhenit'scoldoutside,your heater mayblowoutcoolair.Thisisnormal.Whenyouincreasetheengine If it doesn't,yourcoolant speed,yourheatershouldblowoutwarmerair. level maybe low. See"EngineCoolant'' in theIndex to findout how to check your coolant level. Electronic HeatingAir Conditioning System Function Display K2305 If yourvehiclehasairconditioning,yourheating/airconditioningsystemwill look like this. 3-5