I had a similar situation. Weather got cold. I was unable to put in a correct temp thermostat. I remembered something my father told me about about his father's car and how he'd get the engine temp up (this was long ago before there were reliable thermostats). He used a horse blanket over the front grille...the old flat-front radiator with chrome trim around it and the bug-eyed headlights on each side. The horse blanket kept the wind from blowing off the accumulating engine heat. My dad said it worked pretty good - back in the day. I tried something similar. I took a piece of card board, cut it to the shape of my volvo grille, punched some holes in it (to use zip ties to attach it to the grille). I drove it around, and the temp moved right up to just below mid-range. I was even able to use the heater without any problem. Went all winter with the car like that. Worked like a charm. When warmer weather came, I installed a new T-stat.

Hope this helps your son - even a poor college student could do this...wait, especially a poor college student could do this.