Well First off I'd replace thermostate, while your at it drain and flush
radiator. Also if the Heater still continues to blow cold that could mean
a bad heater core which can be a pain to replace. An option is to bypass
the heater core by taking the two hoses off and coupling them together. I
had overheating issues and no heat, did the following and haven't had any
issues yet. One downfall is no heater in the winter, being the lazy man I
bought a power inverter and space heater to keep my car warm, hey it works
>> Stay informed about: overheating