Are you getting any Check Engine lights? A low-speed fan fault will cause a 5-1-4 code and trigger a Check Engine light. You'd probably also get a flag from the ECM overheating. Turn ON the A/C switch and when the compressor is running you should see/hear the fan come on. If you let the motor warm up long enough or look at it after you've come back from driving, pop the hood and you should see/hear the fan running. How old is it? They sell just the motor for about $100 or so online. If you want to replace the whole fan it cost about $250. Depending on the age of the car if the fan is working and the thermostat is good (make sure the thermostat has a bleeder hole in it) , it is more likely a radiator clogging (efficiency) problem. This is commonly caused when people use regular garden hose water in the system rather than distilled water from a jug and after a while the minerals build up and clog up the radiator core. A new radiator is about $300. Do a couple of these checks and let us know what you find. Mike