The thermostat is basically a temperature controlled valve which is installed in your coolant system. When your engine gets hot enough, the valve opens and allows your coolant to flow through the radiator and keep the engine from over heating. The thermostat is USUALLY located on your engine where the upper radiator hose connects. The metal part that the hose is clamped to is usually held to the engine by two bolts. The thermostat is located under that. I know of one person on AB who has a subaru and says his is on the engine where the BOTTOM radiator hose is connected. This is the first time I'd heard of that as a location. If you aren't sure, look in a Chiltons', Haynes, or Mitchell's maintenance manual for your car (auto parts stores have these for about $20) or call a repair shop and ask. Thermostats cost less than 10 bucks at the parts stores. If your car requires a gasket you need to get one of those too, they cost a buck or two. And you'll need some gasket sealant, a tube of which typically costs less than 5 bucks. My wife's old Explorer used a rubber gasket that fit around the thermostat, which meant I didn't have to buy a paper gasket and sealant. If you do the work yourself, you are looking at less than 20 bucks in parts. Usually it doesn't take much to change the thermostat...depends on whether or not you have to remove anything to get to it first. First time you do it may take you an hour or so. By the way, check your radiator hoses...if they need replacing, this is a good time to do it. Especially since you will be disconnecting one of them for this job and if it's old and brittle it may crack. They don't cost much either...probably 20 bucks or so, depending on hose length and what-not. If you have the shop do the work for you, you are looking at parts plus probably an hour's labor at whatever rate they charge. Which may be around $45/hr.