How to Replace the Thermostat in a Chevy Vanby Chris Moore; Updated November 07, 2017
Items you will need
If your Chevy van is having temperature problems, the thermostat could be the cause. If the thermostat is stuck open, the engine will take a long time to warm up. If the engine overheats, it can be because the thermostat is stuck closed; if this is the case, the engine will be hot, but the upper radiator hose won't be. A stuck thermostat cannot be fixed; it must be replaced.
Disconnect the battery's negative cable as a precaution against electric shock.
Drain the engine coolant by placing a container under the radiator's drain plug and removing the plug with a wrench. Drain about 2 qt. of coolant. If you don't get this much from the radiator, move the container to the drain plug at the engine block and remove that plug.
Remove the air cleaner assembly by detaching the fresh air intake duct from the housing assembly's mouth and removing the air cleaner's cover nuts or wing nut with the wrench.
Loosen the clamp connecting the upper radiator hose to the thermostat housing cover -- pliers can help -- and detach the hose from the cover.
Detach the thermostat housing cover by removing its bolts with the wrench. The thermostat is seated within the housing.
Lift the thermostat out of the housing. Pay special attention to how the thermostat is installed -- specifically, which end is facing up.
Scrape away all of the old gasket material and sealant from both the housing and the cover using a gasket scraper. Clean off the surfaces with acetone or lacquer thinner.
Apply a thin layer of RTV sealant to the mating surfaces on both the thermostat housing and its cover.
Install the new thermostat into the housing, making sure its correct end faces up. The thermostat's spring should point down into intake manifold or lower housing.
Connect the cover to the housing by placing a new gasket on the housing with the bolt holes lined up, installing the cover on the hosing and installing the bolts. Tighten the bolts to 15 to 20 foot-lbs.; make sure you don't overtighten them.
Reconnect all other parts in reverse order of removal.
Refill the engine coolant. You can use the old coolant if it isn't contaminated in any way; otherwise, use fresh coolant.
Run the engine after installation and check for coolant leaks at any of the places where you removed plugs, connectors or sealants.
Check other areas before replacing the thermostat to make sure if it's the problem or not. Check the coolant level, the tension on the drive belts and the operation of the temperature gauge.