I know with mine, until the engine reaches operating temp it will puff out a lot more black smoke than usual. My last snow trip past Marysville, the water temps got down as low as 45c on the downhill run and then along the flats out of there it was like puffing billy until the water temps got back up there. The weather is warming so I wont even bother with putting a hotter stat in. But then again, Im curious to see if a hotter stat will benefit or not during the warmer months.