I have a 91' Panama 80 series i just got out of the shop with a fresh rebuilt engine. I am having issue with the heater as it doesnt heat more than a few degrees. The hotwater line going into the heat exchanger seems to be hot as well as coming out. Any thought to the problem? What degree thermostat is need to produce heat? Would a 80's series cruiser from Panama have a defirent heater set-up? Thanks in advance for your help. M.P.