I actually bypassed the valve by runing the hose connected to it directly into the heater core. I now have minimal heat again and it doesn't appear to be a thermostat since the truck has run mid range through the summer and now when its cold. The hose that was going into the valve and now directly into the heater core gets hot as well so i know there should be plenty of heat.
BTW Which control opens and closes that valve on the firewall? It's not the heat/cool selector as that runs to the heater core air box.
Originally Posted by joez
On the firewall in the center you will see the valve. Remove the linkage and just wire it fully open. That solved my problem until my heater core clogged up.