Run it on the hose without the Stat and see if it's still heating up. I'd also throw a mechanical Temp gauge on to double check the temp. I don't trust electric gauges. I ran mine on the hose for fifteen minutes Saturday and couldn't get the engine over 140. My stats are 140ís. Next winter you need to put a water pressure gauge on the Foul so you don't have to second guess if your impellor is good.