GDubs280

I just wanted to add to this post for anyone who comes across this thread. I had the same issue with my valve. After I changed the round seal on top of the plunger the top sealed fine but the plunger wouldn’t seal at all so the temp lever couldn’t regulate the flow of coolant. Just full coolant flow all time. On mine, the mechanism sitting on top of the plunger has a screw right on the front that seems designed to fix this exact issue (see pic). By turning that screw clockwise the plunger is raised so that its top position begins higher in the valve body. I simply turned it and blew into the other side until it sealed up. Worked great. I know there are a lot of differences among the years for these valves, mine is a November 77 build date, so in case anyone has the one pictured below, definitely try this first.