Location of 2001 Chevrolet S10 4.3 engine thermostat?

The thermostat on a 2001 Chevrolet S10 with the 4.3L V6 engine is located at the rear of the engine, on the passenger side. It's usually housed in a plastic or metal housing at the back of the engine block, near where the upper radiator hose connects. You'll likely need to remove some components to access it easily, such as the fan shroud. A repair manual specific to your year and model will give precise details and diagrams.