Do you know the history of this car?
Or is it fairly new to you? If so, then you cannot assume anything.
Overheating while driving is a flow problem.
As already mentioned, replacing the thermostat is quick and inexpensive. Don't be tempted to use a 160. Factory spec is 177-184.
Brown coolant isn't good. Flush radiator, hoses etc. and refill with 50/50 green stuff. Prestone, Prestone, who needs Prestone? Good to replace every 3 years or so.
If there's no joy after that, you may have worn/rusted water pump impellers. Another quick check and fix. (Rockauto)
Last and most expensive is pulling the radiator to get it checked/cleaned by an old fashioned radiator shop.
Slants run just fine with factory equipment in good condition. No real need for shiny aluminum rad and shroud. (Especially in Maine!)
Looks like you have a nice car. Lotsa fun in the summertime.
