COLD START FAN NOISE (INSTALL REVISED FAN CLUTCH)

SUBJECT: COLD START FAN NOISE (INSTALL REVISED "QUICK DUMP" FAN CLUTCH)

MODELS: 1987-92 M-VANS WITH 4.3L ENGINE 1990-92 L-VANS WITH 4.3L ENGINE 1988-92 S/T TRUCKS WITH 4.3L ENGINE

THIS BULLETIN CANCELS AND REPLACES GMC TRUCK BULLETIN 92-6B-56. IT IS BEING REVISED TO INCLUDE M/L VANS, AND TO ADD SERVICE PARTS INFORMATION AND RPO DEFINITIONS. ALL COPIES OF 92-6B-56 SHOULD BE DISCARDED.

CONDITION

Some owners of 1987-92 M-vans, 1990-92 L-vans, and 1988-92 S/T vehicles with a 4.3L engine (RPO LB4, LU2, or L35) and air conditioning (RPO C60) may experience higher than normal fan noise upon cold start up (usually fan noise extended beyond 90 seconds after start up).

CAUSE

This condition may be due to an extended engagement of the fan clutch.

CORRECTION

The condition may be corrected by installing a revised fan clutch which reduces the fan clutch engagement cycle. Vehicles built after the following VIN breakpoints have the new fan clutch installed in production:

Plant VIN

Moraine N2514836 Shreveport N8512403 Pontiac West N0508347 Baltimore NB534465

SERVICE PROCEDURE

Refer to section 6B1 "FAN CLUTCH REPLACEMENT" in the appropriate Service Manual for removal and installation of the fan clutch.

Important

To maintain a balanced fan assembly, align the yellow paint mark on the fan clutch with the yellow paint mark on the water pump hub (Figure 1).

SERVICE PARTS INFORMATION

Model Year RPO Part Number Description ----- ---- --- ----------- ----------- S/T 1987-92 LB4, L35, C60 15672779 Fan Clutch M/L 1990-92 LB4, LU2, C42 22073413 Fan Clutch M 1988-89 LB4, C41, C42 22073413 Fan Clutch M/L 1990-92 LB4, C60, K01 22124525 Fan Clutch LB4, GT4, C60 (EXC KO1) M 1989 LB4, C60, GT4, (EXC K01) 22124525 Fan Clutch LB4, C60, K01 M 1987-88 LB4, C60, GT4 22124525 Fan Clutch M/L 1992 L35, C60 15674644 Fan Clutch M 1990-91 LU2, C60 15674644 Fan Clutch M/L 1990-92 LB4, C60, GU5, GU6 (EXC K01) 22124526 Fan Clutch M 1988-89 LB4, C60, GU2, GU4, GU5, GU6 22124526 Fan Clutch M 1987 LB4, C60 (EKC GT4) 22124526 Fan Clutch

Parts are currently available from GMSPO.

RPO DEFINITIONS:

C60 - AIR CONDITIONER, FRONT, MANUAL CONTROLS C41 - HEATER, OUTSIDE AIR W/FAN AND DEFROSTER C42 - HEATER, DELUXE GU2 - AXLE REAR 2.73 RATIO GU4 - AXLE REAR 3.08 RATIO GU5 - AXLE REAR 3.23 RATIO GU6 - AXLE REAR 3.42 RATIO GT4 - AXLE REAR 3.73 RATIO K01 - FAN CLUTCH DRIVE LB4 - ENGINE, 4.3L, (4.3Z), V6 LU2 - ENGINE, 4.3B, (4.3B) V6 HI-OUTPUT TBI L35 - ENGINE, 4.3L, (4.3W) CENTRAL PORT INJECTION V6 90 DEG

WARRANTY INFORMATION

For vehicles repaired under warranty, use:

Labor Op Labor Time -------- ---------- J3390 See Applicable Labor Time Guide

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.