Where does the thermostat go on a 1987 VW Quattro 5-cylinder?

The thermostat on a 1987 VW Quattro 5-cylinder is located on the engine block, at the rear of the engine, near the firewall. It's a somewhat difficult location to access and typically requires removing some components to get to it. You'll likely need to consult a repair manual specific to that year and model of VW Quattro for detailed instructions and diagrams showing its exact placement and the necessary removal procedure.