C 1500 Truck 2WD V8-350 5.7L (1989)
Coolant: Technical Service Bulletins
A/C - Apparent Leaks At the Heater Core
GMC NUMBER: 89-T-42
GROUP: 6B - Engine Cooling
DATE: April, 1989
CORPORATE
NUMBER:966201
SUBJECT: APPARENT COOLANT LEAKS AT THE HEATER CORE
MODELS: 1988-89 C/K TRUCKS
THIS BULLETIN CANCELS AND REPLACES GMC TRUCK SERVICE BULLETIN 89-T-42 DATED MARCH 1989, ALL COPIES OF WHICH
SHOULD BE DISCARDED
Some 1988-1989 C/K trucks may experience coolant leaks into the passenger compartment, some of which are being misdiagnosed as heater core leaks.
Potential causes of this condition may be insufficient hose clamp pressure and/or incorrect heater hose position.
Repair Procedure
Figure 1
Pressure test the system to 15 psi and visually inspect the position of the heater hoses. If the leak is around the hose clamp, the system may show no
pressure loss during this test. Both hoses should be located 3/8" away from the cowl gasket (See Figure No. 1). If the hoses are pushed up tight against
the cowl gasket, there is the potential for coolant leaking past the clamp to enter the passenger compartment.
Condition # 1
If the hoses are located 3/8" away from the cowl gasket, torque hose clamps to 2.2-2.8 N-m and pressure test system to 15 psi.
Condition # 2
If the hoses are not located 3/8" away from the cowl, perform the following service:
1.
Cool and depressurize the cooling system.
2.
Disconnect both hoses from the heater pipes.
3.
Cut off the end of the hoses to remove the area deformed by the hose clamp.