I bought a new cap for the x5 and it was a tight fit. I didn't screw it in all the way as a result and water came spewing out once it got hot. hopefully that's all it is on yours.

If your temp gauge is remaining normal and your heater continues to blow hot air when needed its probably a cap or the expansion tank it screws into. Have seen many tanks crack. If the temp gauge goes high suspect the map thermostat and if your heater stops blowing hot air its usually a sign of air in the system which can mean $$$... Get it to the dealer for a check over...

A new cap was fitted but it still happened so with closer inspection ther was a small hair line crack in the headertank so this is being replaced tomorrow.

Good pick up!

I couldn't understand why the dealer didn't pick up that the coolent was spewing out and why it didn't happen on the test drive. It would seem that the previous owner knew this was happening and tightened the coolent cap so tight to try and stop the coolent coming out of the crack that a wrench was needed to undo it. So when the dealership checked the coolent levels they put the top on as normal which meant as soon as we drove the car away the the coolent started coming out of the crack again......at least it sorted now and my wife can enjoy all 4.4 litres of her dream car....and what a fantastic car ir is.

The coolant reservoirs crack easily, fortunately it's not an expensive part and it's easy to fix.