ENGINE OVERHEAT WHEN TOWING OR DURING HEAVY USAGE

Subject: ENGINE OVERHEAT WHEN TOWING OR DURING HEAVY USAGE

Model and Year: 1988-91C/K WITH 5.7L ENGINE

THIS BULLETIN CANCELS AND SUPERCEDES DEALER SERVICE BULLETIN NO. 91-145-6B, DATED DECEMBER 1990. THE LABOR OPERATION AND LABOR TIME HAS BEEN CHANGED, THE FIRST PARAGRAPH UNDER THE FIRST NOTE HAS BEEN DELECTED. STEP 13 HAS BEEN CHANGED AND TWO NOTES UNDER STEP 27 ADDED. ALL COPIES OF 91-145-6B SHOULD BE DISCARDED.

Some 1988-91 C/K trucks equipped with 5.7L engines may experience an engine overheat condition (245 degrees F - 260 degrees F) while towing a trailer or under heavy usage, yet during normal operation, without heavy load or trailer, the engine operates at a normal temperature (21 0 degrees F - 235 degrees F).

If this condition is encountered and cannot be repaired using procedure in the service manual, a larger capacity cooling system may be installed. This larger capacity cooling system typically reduces engine operating temperatures by 20-25 degrees while towing a trailer or under heavy usage.

IMPORTANT: This larger capacity cooling system is not intended for correcting engine overheats that occur while idling or under normal operating conditions.

NOTE: It will be necessary to install new engine oil cooler hoses on models equipped with an internal (inside radiator) engine oil cooler.

On models with an externally (outside radiator) mounted engine oil cooler, the installation will require the removal of the external oil cooler and hoses. They will be replaced by the internal (inside radiator) engine oil cooler, which this larger capacity radiator features, and the required oil cooler hoses.

SERVICE PARTS INFORMATION:

Quantity Part Number Description

1 52457632 Radiator (auto & manual trans) 1 15650248 Shroud (upper) 1 15650247 Shroud (lower) 2 15553981 Insulator (upper) 2 15591853 Insulator (lower) 1 15574276 Bracket (right) 1 15574275 Bracket (left) 1 15627103 Radiator Hose (upper) 1 15629092 Radiator Hose (lower) 1 12076298 Protector (lower radiator hose 1 15574167 Baffle 1 15552389 Deflector 3 11513687 Bolt (rad. support baffle) 2 11509363 Bolt (rad. mounting bracket) 1 15611492 Hose (outlet) "C" models 1 15623000 Hose (inlet) "C" models 1 15611493 Hose (outlet) "K" models 1 15622999 Hose (inlet) "K" models

Parts are currently available from GMSPO.

INSTALLATION PROCEDURE:

1. Disconnect battery. 2. Drain cooling system. 3. Remove upper radiator shroud. 4. Remove upper and lower radiator hoses. 5. Remove heater hose and overflow tube. 6. Disconnect transmission oil cooler lines from radiator. (automatic transmission only). 7. Remove engine oil cooler lines (if equipped). 8. Remove external engine oil cooler (if equipped). 9. Remove radiator. 10. Remove lower radiator shroud. 11. Remove fan and clutch assembly 12. Remove lower radiator insulators (rubber mounts). 13. To enlarge the radiator core support opening to the dimension shown in Figure 1, mark the sections of the core support to be removed and remove the sections, using a suitable tool (panel cutter, die grinder with cut-off wheel, panel knibler, etc.). The core support openings are stamped and can be used as a guide. When cutting the lower corners, it is important to leave a small triangle shaped section for proper radiator support rod attachment. The edge of the new opening must be painted to prevent corrosion. Use P/N 1052820 or equivalent. 14. Install new lower radiator insulators for larger radiator in outer slots (holes) of lower radiator support (see Figure 3). 15. Install new radiator support baff le (see Figure 2). 16. Install new lower radiator shroud. 17. Install new radiator assembly. 18. Install fan and clutch assembly. 19. Install new upper radiator insulators and retaining brackets (see Figure 3). 20. Connect transmission oil cooler lines to the radiator

NOTE: It may be necessary to slightly bend both transmission oil cooler lines in order to obtain proper alignment with the radiator.

21. Install new engine oil cooler lines (if equipped). Refer to Dealer Service Bulletin No. 89-200- 6A for proper installation. 22. Install new hose protector on new lower radiator hose and install new hose assembly.

IMPORTANT: When installing the new lower radiator hose assembly, it is important that the hose protector be positioned correctly in order to avoid any direct contact of the hose with other components.

23. Install new upper radiator hose. 24. Install heater hose and overflow tube. 25. Install new upper radiator shroud. 26. Install new upper radiator air deflector (see Figure 2). 27. Transfer all labels from old upper shroud to new upper shroud.

NOTE: If labels cannot be removed successfully, order replacement labels from GMSPO using the part number printed on the original label.

If replacement campaign labels are required, refer to current copy of "Dealer Follow-Up Campaign Bulletin" for information on blank campaign completion labels.

28. Refill cooling system and check for leaks. 29. Reconnect battery.

WARRANTY INFORMATION

For vehicles repaired under warranty use:

Labor Operation: T7221

Labor Time: 1.4 hrs.

Add: 0.5 hr. if necessary to replace engine oil cooler lines.

NOTE: Labor Operation is coded to base vehicle coverage in the warranty system.

Trouble Code: 92

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.