Go out of town suddenly temperature meter on top but no over heating, bring to Mr Lube and they replace the thermostat with aftermarket one. Seem okay for about a month when driving in town then its acting up again, temperature going up and down and loosing the heater. Replacing with OEM thermostat seem okay and when going out of town the temperature acting up again but no over heating. Replacing water pump in last view days l look okay for now. Any idea? Thanks