because you have an engine alarm doesn't necessary mean that it's a heating issue. The way you started off your question, or the way I interpreted your post kind of led me down a rabbit hole. His oil pressure pressure switch could just as easily be what's giving him his alarm. I would change the pressure switch. If he doesn't want to spend the money for a new pressure switch, I would remove one on the wires on the switch while the alarm is in. If the alarm goes away then it's most likely an oil pressure switch.