REAR MAIN OIL LEAK DIAGNOSIS

1987 PARISIENNE AND GRAND PRIX VEHICLES EQUIPPED WITH THE 4.3L (VIN CODE Z) ENGINE

Some 1987 Parisienne and Grand Prix vehicles equipped with 4.3L engines with engine build date codes prior to T1202 may experience a rear main oil seal leak condition due to a poor surface finish on the crankshaft sealing surface. Engine date codes are stamped on a pad at the block to passenger side cylinder head parting line, see Figure 1. The build date codes may be found in this area and appear as shown in the following example:

T1202ABC

The first letter indicates the plant where the engine was manufactured, the next four numbers indicate the date of manufacture, in this case, 12th month 2nd day, and the last three digits may be any broadcast code.

Check the oil leak using an ultraviolet light and engine oil dye. If leakage between the crankshaft sealing surface and the crankshaft oil seal lip is indicated, the crankshaft sealing surface finish should be inspected using the following procedure:

1. Remove the rear main seal and seal retainer using procedures in Section 6A3 of the appropriate service manual.

2. Using a bright light, shine the light across the crankshaft sealing surface. A normal sealing surface finish will have machining marks in a circumferential direction (which direct oil toward the inside of the engine) with no crosshatch machining marks (which direct oil toward the outside of the engine) or scoring present. If there are crosshatch machining marks or scoring present in the surface finish, the crankshaft must be replaced. Use the procedures in section 6A3 of the appropriate service manual.

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.