I figured it out Philip !! Thanks for the info I had the send and return lines crossed both send to the back both return lines to the front that's why it wasn't working. Finally looked at it enough! Lol
Yes, or apply pressure to the overflow tank with the return line(cab heater) disconnected (controlled and cold)... ... Philip
Glad you figured that one out sure was a head scratcher. Never a bad idea to snap a few pics before you take stuff apart if you don't do it every day.