2018 mPACT Retriever 1000 Diesel overheat problems

has anyone had an overheat issue with their diesel? I took it in and tech said he could not get it to show overheat but the next time I used it I was just sitting still idling and it gave overheat error. Temp jumps all over the place on the screen. Antifreeze level is good and I only have 250 hours use. Seems like it would be a thermostat issue but I don't know what to check to diagnose the issue. I've already had to replace the starter so it feels like I may have a lemon!!