This is for my 260E...Fan clutch does not lock. No roaring at all, that is how I know it is not turning on. I am familiar with the roaring noise because my wagon does it all the time on hot days -- This car is dead quiet.

Is that just the fan clutch (viscous fan coupling -- same thing?) or could it be anything else?

I replaced my engine temp sensor at the back of the head, so its not that.

Yep it is danger zone which is why was I was very concerned and tried to get off the freeway ASAP and had the heater blasting (No A/C for me yet...as evap is leaking so I couldn't turn on Aux fan). Once I got off the car was sooo...slowww to accelerate. I got her back down into the 85C range quite quickly though where she stayed.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k