Where is the thermostat on a 2003 es300?

On a 2003 Lexus ES300, the thermostat is located in the engine compartment, specifically on the engine block near the water pump. To access it, you typically need to remove the engine cover and possibly the air intake duct. The thermostat is housed in a housing that is secured by bolts, and it is connected to the cooling system hoses. Make sure to drain the coolant before attempting to replace the thermostat.