In the immortal words of one of Batman's arch-enemies...."riddle me this"

My son's 84 Vanagon will overheat in the summer when driven slowly....and
in the winter he barely gets heat. Is it the water pump....is it the
thermostat or is it both?

He's coming home from Rochester NY for Thanksgiving this week and I want to
see if I can send him back with a bit more heat than he's had in the past
year or so....

Thanks.

Ric