C 3500 Truck 2WD V8-8.1L VIN G (2001)
Heater Core: All Technical Service Bulletins
Coolant Flow Restrictor - Whining Noise
File In Section: 06 Engine/Propulsion System
Bulletin No.: 01-06-02-002
Date: March, 2001
TECHNICAL
Subject:
Whining Noise In Passenger Compartment When Engine RPM Is 1700-2300 (Remove Coolant Flow Restrictor)
Models:
2001
Chevrolet and GMC C/K Models (Silverado, Sierra) with 8.1 L Engine
(VIN G - RPO L18)
Condition
Some owners may comment on a noise that only occurs with the thermostat open and can be heard in the passenger compartment only. The noise will not
be heard from the outside of the vehicle. The noise is described as a whining noise heard as the engine operates from 1700 to 2300 RPM. The noise is
RPM sensitive and will change pitch when the RPM is varied.
Cause
Inside the fitting on the coolant crossover there is a rubber washer used as a restrictor. The washer actually creates unusual flow characteristics which
result in a noise that is transferred through the heater core. The condition can be diagnosed by pinching the heater hose with a pair of pliers or vice grips.
If the noise goes away, the flow restrictor should be removed.
Correction
Remove coolant flow restrictor using the following procedure:
1.
Remove the air cleaner outlet duct.
2.
Partially drain the coolant level.
3.
Remove the hose clamp and remove the heater hose from the coolant crossover fitting.
