I have a 92-323 with very little heat. Last year I had to scrape the frost off of the inside of the windshield. I've replaced the thermostat and still very little. The temperature gauge sits at cold for the most part but it will jump up to half way and then back down to cold. Could a faulty coolant temperature gauge sending unit cause this? Could it be a blocked heater core? If it's the core, what's the easiest way to get at it to backflush it without taking it out?

Thanks

 

Remove the 2 heater hoses from the firewall and flush the heater core with a garden hose. It usually works.