A/C - Apparent Leaks At the Heater Core

91chevy06

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.


4. Reconnect hoses to heater pipes, leaving 3/8" between the cowl gasket and the end of the hose.


5. Position the hose clamp between the heater pipe bead and the cowl and torque the clamp to 2.2-2.8 N-m.

6. Pressure test system to 15 psi.

For repairs to vehicles under warranty, use the following Labor Operations and Times:

Condition # 1: Labor Op: T7915 Labor Time: .2 Hr.

Condition # 2: Labor Op: T7916 Labor Time: .5 Hr.