For 1990-2009 cars

# NO HEAT AT IDLE OR MINIMIZED HEAT AT ABOVE IDLE SPEEDS

NO HEAT AT IDLE OR MINIMIZED HEAT AT ABOVE IDLE SPEEDS WITH THE SUBJECT ENGINE MAY BE CAUSED BY A BLOCKED COOLANT PASSAGE LEADING TO THE INTAKE MANIFOLD. IF INSPECTION OF THE RELATED COMPONENTS (THERMOSTAT, HEATER CORE, ETC.) REVEAL NO CAUSES FOR THIS CONDITION, CORRECT AS FOLLOWS: (1) REMOVE THERMOSTAT HOUSING. (2) USE A DRILL MOTOR AND 3/8" DRILL BIT. (3) APPLY GREASE TO THE END OF THE DRILL TO CATCH THE CHIPS (4) AT A 30 DEGREE ANGLE BELOW THE HORIZONTAL AND APPROXIMATELY 10 DEGREE OUT FROM THE FACE OF THE HEAD, DRILL THROUGH THE FIRST WALL OF CASTING ONLY (SEE ILLUSTRATION). (5) WITH A MAGNET, REMOVE THE REMAINING CHIPS. (6) INSTALL THERMOSTAT HOUSING. LABOR OPERATION NUMBER: T1072 LABOR TIME: .7 HOURS

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.