Hi, all ready to go on holiday, doing the usual car checks. Tyres, oil, water. Thought the water required just a little top up. So topped the header tank up to half full. Everything hunky dory.

10mls down the road and overheating warning light and message to pull over and idle engine. Lifted the bonnet and saw the header tank bubbling away and steam coming from the over flow. Stopped the car for about 10mins and tried again. Temp went right into the red then all of a sudden fell to normal. Needless to say, I returned home and we used the wife’s car.

has anyone had this sort of reaction by just topping the water up with a cup full of water?

Have you tried replacing the coolant pressure cap as this can cause the issue if it is failing to hold the pressure