I have an interesting one on my 4.6 Vogue. After about 6 miles of driving temp goes straight to max & red light comes on. Then after a short time it drops just as quickly to normal. Fluids seem okay and engine doesn't smell or feel hotter than it should be. Outside temp around zero so not likely to be fan & fan seems to be pulling plenty of air through. I wondered if it might be a faulty sensor. Anyone had a similar experience?First change your thermostat, cheapest option, but could be your water pump