GM 10021199 Housing,Engine Coolant Thermostat

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Testing the thermostat in a far more convenient way can only be possible after it has been removed from the engine. In most cases, if one suspects a problem with the thermostat, then replacing it is less costly as they are not expensive. First remove the thermostat to test it. Check whether there is much rust or corrosion on the thermostat. If either of these conditions exists, install a new thermostat. Put the thermostat into water that's heated 25° above its temperature marking. The water should be at around 220°F (104°C). When immersed in well-agitated water of this type, its valve will remain fully open. Then take out the latter by means of a wire bent and put again into water that is 10 degrees below its mark or about 185 degrees F (85 C). At this temperature, the thermostat valve ought to close completely. Replace it if it's good; otherwise buy another one with a similar temperature rating as before.

For 1982 and later L4 models, the thermostat and housing have been redesigned for simpler servicing. To replace the thermostat, first remove the thermostat housing cap. Then, grasp the thermostat handle and pull it out. Replacement is completed by pushing the thermostat into the housing, making sure it is seated, and installing the cap.

If the thermostat checks out OK, reinstall it.

If the thermostat checks out OK, reinstall it.

Before installation, use a gasket scraper or putty knife to carefully remove all traces of the old gasket on the thermostat housing and the water outlet cover. Make sure not to allow any gasket particles to drop down into the water passage.

The thermostat is designed to open and close at predetermined temperatures to allow coolant to warm up or cool the engine.