I'm guessing the aux fan is toast and that is causing high pressure condition which is tripping the safety cutoff. When it cools off, things work for a little while until it gets too hot and too high pressure again. I Would second the suggestion above that it needs a visit to a mechanic if you want it repaired. And before it blows out something else...

Sadly the fan is not cheap $300-$500 depending on where you get it) and will take some time to replace. If that is really the problem, be prepared for $800-$1000 estimate (one standard BMW increment LOL).

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David.X5
2001 X5 4.4i Sport
SOLD! at 160k miles