Do you have rubber exhaust hose? You may be missing some raw water pump impeller vanes or have a partial blockage. There may be enough water flow for the engine at idle, but the increased fuel burn when the engine is in gear may be raising the exhaust temperature to wear the hose is getting cooked.
I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters