I'm in Arizona in the summer for starters. 1964 volvo 122. Thermostat was replaced about a year ago. I got it from an 'old volvo place' in pennsylvania, they knew their stuff so i assume it was a good one. its a low temp thermo. 140 degrees. before the new thermo used to go hot then come down, and once in a while do it again. since i've been in AZ it tends to just go up after 20 minutes. and it will go all the way, if i turn on the heat i could sometimes smell some coolant coming out of the tube and onto the engine. i just reattached my overflow tank, nothing changed. are you supposed to fill the overflow or just keep filling the radiator until it starts to fill the overflow tank? i know i've got oil pressure. how can i be sure the thermo is opening? when i get home i can hear it bubbling a bit after i shut it off. a guy i work with said it may be the sending unit of the guage is dirty and therefore heating up more. the water pump is ok.
please fill me in with these answers and any other things you think a young 122 owner should know about it. i'm taking her cross country and would like to make sure we've got decent odds.

thanks
rus