HEATER PERFORMANCE CHANGES THERMOSTAT/GASKET P/N'S

VEHICLES AFFECTED: 1984 & 1985 'A' Series With 3.8 L V-6 Engine (VIN Code 3) 1985 'C' Series With 3.8L V-6 Engine (VIN Code 3) 1985 'N' Series With 3.0L V-6 Engine (VIN Code L)

91 deg.C (195 deg.F) THERMOSTAT ON 3.8L V-6 ENGINE (VIN CODE 3) -------------------------------------------------------------- Recent changes on the 3.8L V-6 engine (VIN Code 3) used in the 'C' series vehicles have resulted in changes to heater performance in cold Weather. A 91 deg.C (195 deg.F). high bleed rate thermostat assembly has recently replaced a 82 deg.C (180 deg.F). thermostat.

If a Comment of poor heater performance in cold weather is received, install thermostat part number 3041390, and replace coolant outlet gasket, part number 1250390. Refill engine cooling system with proper coolant and ensure that all trapped air is expelled. Check coolant protection level for adequate protection.

PROPER COOLANT FILL

On the 'A', 'C' and 'N' series vehicles, as well as other models, care should be taken to remove any trapped air from the engine cooling system. Air trapped in the heater core can significantly degrade heater performance and cause heater temperature cycling. To ensure adequate fill and remove trapped air, use the following procedure:

CAUTION:

Use proper precautions to help avoid the danger of being burned when removing or installing radiator cap and when expelling any trapped air.

1. Remove radiator cap. If engine is hot, allow it to cool down until radiator cap can be safely removed. Top off coolant in radiator to within 75mm (3 in.) of the top.

2. Place HVAC controls in A/C mode, or auto on C68, and temperature to highest setting.

3. Start engine and allow it to warm up while idling until thermostat opens. Coolant level in radiator will rise somewhat when thermostat opens. In cold ambients, run until radiator core is hot to the touch.

4. Allow engine to continue idling until lower radiator hose to water pump is hot.

5. Cycle the engine speed up to about 3000 RPM five times, and back to idle. This should expel trapped air in the system.

6. After the air has been expelled, fill the radiator, check the protection level, and install the radiator cap. The fan may not cycle in cold ambients.

7. Fill coolant overflow reservoir to the hot level. Check for any coolant leaks with engine running.

Coolant bypass from the intake manifold to water pump is being added on the 3.8L V-6 engines (VIN Code 3) and the 3.0L V-6 engine (VIN Code L) for coolant temperature cycling.

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.