overheating troubleshooting

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'07 X5 4.8i. Recently overheated in stop 'n go traffic when it was 27C outside. Radiator fan was not on. After it cooled down I was able to drive home on the highway as there was no traffic.



No loss of coolant. When idling the coolant temperature as measured by the hidden dashboard diagnostics climbs steadily past 100C to about 120C before I shut the engine off. Fan does not run (even with AC switched on), and both upper and lower radiator hoses top out at about 99C. One time when I was doing this test I heard a rattling noise which appeared to come from the vicinity of the water pump (which I replaced preventatively 3 years ago), but I haven't been able to reproduce it and put a stethoscope to it.


Suggestions for how to troubleshoot? How can I know for sure that the water pump is working? Can I jumper the fan with 12V to see if it is working, or does it require a signal on the signal wire? Should there be 12V present at the fan connection at all time?