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.





Important:
The simple tool in the picture was made of 3/32 in. welding rod similar to a coat hanger. The tool is designed so that the tip of the tool will thread underneath and dislodge the 0-ring from the back edge of the fitting. The tool is made as tight to the inside diameter of the fitting as possible.

4. Insert a hooked end pick tool, or equivalent, into open end of the fitting. Pushing the tool approximately 2 inches deep in the fitting, and through the restrictor washer, pull and slightly twist to remove the rubber 0-ring.

5. Install the heater hose and the hose clamp on the coolant crossover fitting.

6. Top off the engine coolant system.

7. Install the air cleaner outlet duct on the vehicle.

Warranty Information





For vehicles repaired under warranty, use table as shown.





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