I'm stumped, hope someone can help. '80 242 GT. I went through the engine, replaced the head gasket, new water pump, etc. etc, about 3K miles ago. The entire cooling system was flushed clean a few times, never had a problem until last week.

I headed out, engine warmed up and the gauge kept going up and up, never actually hitting the red but coming pretty darn close (blasted the heater to keep it from going there). I can grab and hold onto either of the radiator hoses, no problem. So I figured it was the 'stat that was stuck closed. I replaced that, no change, same problem.

I swapped out the sender, same problem. I rigged an R-sport temperature gauge up and it went all the way over 100C (interpolating probably 107C). This is after just idling. Again, I can grab both rad hoses and thery are just pleasant hand warmers.

Any thoughts? has something plugged up coolant flow in the head or the block? It's not smoking or leaking so I believe the system is holding pressure. When I crack the cap on the overfill, it hisses a bit but not a whole lot. Again, it doesn't seem like the water in the radiator is that hot.

Many thanks, Frustrated Randy