Why is the cooling fan comes on and off, constantly?

[08AudiSline]

Hi, I'm trying to find out why is my car acting up lately. I own a 2008 Audi A6 Quattro, Ive had it for almost a year now and it has been great. Lately now, when I turn on the car, the cooling fan start to come on and off every 4-6 seconds, constantly with the AC off. Also, I don't know if this related to the same problem, but my car seems to overheat when the AC is on at idling, and back to normal when start moving up to speed. it doesn't happen all the time, but it gets me off guard and confuse. Please help. I'm still in a learning process of DIY.

[A4DK]

Check the condition of your thermostat. Mine did that when it was about to get stuck and required replacement.

[TheAlphadog]

A4DK is right. Your thermostat has failed or is about to fail. I would not drive it much more without getting it replaced. You'll risk damage to your engine. Get ready for a $800 - $1500 repair bill unless you want to do it yourself.