2003 Clio 172
So I had my thermostat and coolant temperature sensor changed a couple of weeks ago along with a complete coolant flush and change due to my temperature gauge dropping a notch or so from halfway, before rising again. This was usually happening on cold or wet mornings down a long hill. I noticed this morning it dropped again going downhill by around a notch, and took a couple of minutes to come back up afterwards. Any ideas what could be causing it? ?