Cooling problem SOLVED

I had this same thing happen years ago on a Chevy 292 powered 8" lake water pump that ran on propane. It had a coil inside the pipe that was cooled by the water that was being pumped and had no radiator. The regulator for the propane would ice up. I chased that problem for a while and finally I woke up one morning about 5 am I went out to the pump and found the impeller spinning. Glad you found yours too!