To those that have a leak--have a system pressure test done to find the leak. If it still doesn't show look for other symptoms like some sweet smelling white smoke out the tailpipe. Most common leak sources and easiest to eliminate are coolant hoses or heater hoses, plastic piece on top of the expansion tank or the tank itself. It could be a Vanos cover leak. That is harder to pinpoint but one strong indication is coolant leaking from the bellhousing.

For those showing a code and don't have a leak, easiest, cheapest and most common potential fix is to replace the thermostat as several have mentioned. I would do that first.

Unless the engine has run hot for an extended period time you may never have to replace some of the parts in the cooling system.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas