Question #2, you're not going to hurt a 3208, or any diesel for that matter running at 155 to 160 degrees, that's actually too cold, that is if the temp gauge is reading correctly.
Question #1, that's not an "overflow" line. If I recall the 3208 correctly, it has a bleeder valve on the top of the injection pump to purge air when repairs to the pump have been made. If I'm correct, that "leaking" hose should be connected to a valve on top of the injection pump, a small shut off valve. If that's what is there, you have either a shut off valve that is not closed completely, or it's faulty, there should be no fuel leaking from that tube.