Thermostat Test Procedure Using Glycol

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Inspect the operation of the thermostat by hanging the thermostat on a hook in a 50/50 percent solution of DEX-COOL® and clean drinkable water.

In order to inspect if the thermostat valve is opening properly, perform the following test:

Completely submerge the thermostat in the glycol solution. The solution should be 11° C (22° F) above the temperature indicated on the thermostat valve.
Thoroughly agitate the solution. Under these conditions, the thermostat valve should open.

Fig 1: View Of Thermostat Test Procedure Using Glycol

Courtesy of GENERAL MOTORS CORP.

In order to inspect if the thermostat valve is closing properly, perform the following test:

Completely submerge the thermostat in a glycol solution. The solution should be 6° C (10° F) below the temperature indicated on the thermostat valve.
Thoroughly agitate the solution. Under these conditions, the thermostat valve should close completely.