I got my thermostat replaced. On its first or second day, the temp stays around 89-90 degree most of time. Then the following days, it varies from 65-80 on highway, 84-94 on local. Outside temp is about -10 degree these days.

Is this normal? Do you guys have a steady 88 degree most of time?
I purchased thermostat from ebay with under $40. My local dealer asks more than $150.
Where do you guys buy it from?
I doubt the one I bought does not have a good quality...

Thanks.