Engine - Rear Main Oil Leak Diagnostics
87chevy19GMC NUMBER: 88-T-46
GROUP: 6A - Engine Mechanical
DATE: October, 1987
CORPORATE
NUMBER: 866101R
SUBJECT: REAR MAIN OIL LEAK DIAGNOSIS
MODELS: 1987 R/V, G, M AND 1988 C/K MODELS EQUIPPED WITH 4.3L (VIN CODE Z) ENGINES
THIS BULLETIN CANCELS AND SUPERSEDES TRUCK SERVICE BULLETIN 88-T-7, DATED MARCH, 1987, ALL COPIES OF WHICH SHOULD BE DESTROYED.
FIGURE NO. 1:
Some 1987 R/V, G, M and 1988 C/K trucks 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. Note - Engine date code location is shown in Figure No. 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 day of manufacture, in this case, 12th month 2nd day, and the last three digits may be any broadcast code. To diagnose this condition, check the oil leak using an ultraviolet light and engine oil dye. If ALL of the following conditions are met, replace the crankshaft and rear main oil seal.
1. Leakage is between the crankshaft sealing surface and crankshaft oil seal lip.
2. Engine build code is prior to T1202. (See explanation above).
3. Removal and inspection of the rear main oil seal indicates the seal is not torn.
If all of the above conditions are not met, replace only the rear main oil seal and retainer.
NOTICE: THE ASSEMBLY OF THE REAR MAIN OIL SEAL AND RETAINER MUST BE PERFORMED IN THE FOLLOWING SEQUENCE OR POTENTIAL FOR AN OIL LEAK AT THE REAR MAIN OIL SEAL EXISTS.
1. LOOSEN OIL PAN FASTENERS AND ALLOW OIL PAN AND OIL PAN GASKET TO FALL FREE OF REAR MAIN OIL SEAL RETAINER.
2. INSTALL NEW REAR MAIN OIL SEAL AND RETAINER. TORQUE RETAINER FASTENERS TO SPECIFICATION.
3. AFTER TORQUING RETAINER FASTENERS, TORQUE OIL PAN FASTENERS TO SPECIFICATIONS.
IF THIS PROCEDURE IS NOT FOLLOWED, THE OIL PAN MAY INTERFERE WITH THE RETAINER AND NOT ALLOW THE REAR MAIN OIL SEAL TO CENTER ON THE CRANKSHAFT.
This condition was corrected in production effective with the following VIN breakpoints:
1987
Flint GMC HF712338
Chevrolet HF345461
Janesville GMC HJ515177
Chevrolet HJ138800
Baltimore GMC HB512872
Chevrolet HB150460
St. Louis GMC HS515759
Chevrolet HS144963
Lordstown GMC H7512809
Chevrolet H7138970
Scarborough GMC H4507505
Chevrolet H4114959
1988
Fort Wayne GMC Z500019
Chevrolet Z100022
Pontiac GMC JE500221
Chevrolet JE100451
Oshawa GMC SOP
Chevrolet SOP