How freely should the viscous fan spin?
Posted: Sat Apr 03, 2004 5:51 pm
I just removed my viscous fan wondering how freely it should spin. It seems quite tight , in other words it doesn't spin freely whilst holding the nut. 
It seems the viscous fans only free wheel once the engine speed has been above around 2,000 RPM for more than a couple of minutes and the oil inside it has warmed up (this coincides with engine temp, no point having the fan on before the thermostat has opened).
So, when you come to a stop and the engine idles for a bit, you will hear the fan making a noise like a freight train for a couple of minutes after you have started moving again. Then it will rely on the movement of the vehicle to put enough air to the radiator (and the fan will still spin a little to help direct the flow).
If it's not doing this, then a new one will be a necessity.
