Mine did it when I took off the radiator cap and checked the level and made sure I tightned back good. I must have got air in the system somehow, anyway I refilled and (burped it) as the shop manual said and put a little watter wetter in it and filled the overflow tank to the low level, started it up to full operating temp and topped off the tank to just below the high mark. have'nt had a problem since then its been about three months. If that does'nt work take it to the dealer and let him check it out. could be thermostat or ?