Where is the thermostat located in a 2001 Highlander?

The thermostat located in a 2001 highlander is between the exhaust manifold and the alternator. You will come across many issues with an engine. A spark plug may come off, causing engine issues. A gasket may become loose and that needs to be tightened up. You can have oil leaks and those need to be repaired quickly. A really serious problem is the engine overheating. This may lead to fires and the car exploding. There could be excessive oil use, requiring the oil to be replaced sooner than expected. The coolant needs to be changed every 60,000 miles or so. Your air filter needs to be changed every 15,000 to 30,000 miles or so. The spark plugs need to be changed every 100,000 miles unless it's a copper one. A cooper spark plug needs to be changed every 30,000 miles.