on my 2.7t a6, this time its the cooling system, my temp gauge had its own mind, so i thought i would try and fix by replacing the sensor/sender so i bought one off flea bay and went to fit it, but got confused, as i thought it was at the back of the engine, under the intake pipe (a pipe kind of sticking up) but the actual sensor was different to the one i bought, so i thought i'd ordered the wrong one, but then i noticed another one at the front, on the bottom radiator hose which was the same as the one i bought, so i changed it, but hasnt fixed the problem. So, my first question's are, what is the one at the back? and what is the one at the front? Also a quick question on the viscous fan, as at low revs you can hear the fan "howling" and gets louder as you go up the revs, i know this is normal but when i get to exactly 2800 rpm it all goes quiet (guessing it just slows down) but why? i thought it would just keep getting faster and faster all the way up the rev range?