I have been having issues now for about a month where it takes forever for my van to warm up. The temp Guage will go up to just past the 3/4 mark on the Guage towards high for a minute or so then back down to a few marks under normal. Just the other day however heat hasn't worked at all and the temp Guage now regularly goes higher, fans kick on when it does so, and I am just not sure what to do. I live in ND where temps can get to negative digits so I need heat, even if it isn't super hot.

Is it the thermostat sensor or possibly something else? If it's the thermostat, how easy is it to replace and cost wise how bad? Im a 5ft nothing short armed lady so hoping i can do it myself.