1997 C36 warm air problem (thermostat?)

[Rocky]

Hi guys,

It's been REAL cold these past couple days up in Toronto. It was 3 Degrees Farenheit last night. I was having problems with not getting hot air. It comes out warm at intervals. The engine temp never went above 80 and kept fluctuating between 75-80 whether i'm on the highway ro on the normal streets. Anyone else have this problem before? Could it be a bad thermostat? Is it easy to fix?

Thanks guys,