Where is the thermostat on a 1999 Chevy Geo Prism?

On a 1999 Chevy Geo Prism, the thermostat is located in the engine compartment, typically near the engine block where the upper radiator hose connects to the engine. To access it, you'll need to remove the upper radiator hose and the thermostat housing, which is usually held by a couple of bolts. It's advisable to allow the engine to cool down before attempting to replace the thermostat to prevent burns or injuries.