This seems to be a problem in all weather conditions, mainly over 32 degrees F. A loud fan will come on and stay on as soon as the temp needle goes a tick over 80 on the engine temp gauge. It is really annoying! It slows down the car a lot and is very noisy. It does it with the A/C on or off. The coolant was flushed last year at 36k miles. Truck now has 48k and it has been doing this noise since about 28-30k miles. Any ideas what it is? It sounds like a school bus. btw, the temp gauge never goes above like 80-85.

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2003 C320 4matic (C2, C3, C4)
1999 ML320 (ML55 headlights, MY00 door seal update, ML500 grille, chrome bull bar)