1990 geo prism, mileage: 160,000. When I drive this car more than four miles, the needle gauge always goes to hot. A friend of mine already changed the thermostat and it still does the same thing. What other factors contribute to this problem? What should be done?
You did not mention if your car is losing coolant, so we assume it is not. Does the electric fan cycle on when the temperature is up? If not check fuses, temperature sensor and relay. You may be overheating due to a partially plugged radiator. A radiator repair center can check that for you and if necessary remove and clean the radiator.