Interesting, as I I’ve been diving into understanding this component to decide if I should replace it.
The thermostatic fan is an amazing bit of engineering. The special oil can leak out and there is videos of rebuilding and replacing the oil.
The oil emerges from is central reservoir via a thermostat valve and is driven by centrifugal force to fill the outer capillaries and bind the fan into turning with the engine (bit like an auto gearbox TC). When the temp drops it gets trapped back in the centre reservoir and the fan freewheels.
Now, what I don’t know is if the traditional non electronic thermostat (bimetallic strip or similar) is fully replaced or augmented electronically in the Disco?
What I do know is that the ‘rule of thumb’ test of listening for the roar on cold startup is common to all thermostatic fans as the oil leaks out at rest until on startup it is forced (spun) back into its reservoir on startup until it freewheels until it’s needed.
It is not signifying IMHO that the ECU is doing a test on it. It does indicate the oil is present and circulating normally.
I’d be keen to understand how the electronic aspect interacts and if it just overrides the thermostat or replaces it?
It does not seem also to have the ability to operate partially. Once the oil is out it’s either locked or freewheeling.
The old test used to be shove a rolled up newspaper at the fan. If the fan stopped the clutch was done, if you ended up with confetti it was fine.
I've not looked into the mechanical aspect of how it works, but the ECU modulates the control valve to give proportional control of the fan. I've sat at constant RPM and watched the fan RPM vary with the varying control duty cycle.
I always thought the roar on startup was the cold thick oil and as it warmed up the fan dropped into a controllable state. That's how it works on my other car with the thermo-viscous coupling.
They are awesome things.
I don,t really know, but once I was doing some work on the cooling system and I disconnected the cable to the fan. When I completed the work and reconnected the fan it did not cut in when the engine first started. At the time I did not have a code reader so it was a few days before I could get my Indi to check the problem. For those few days the fan never once cut in at start up. When the Indi checked there was a fault code showing which he cleared and then the fan started working again as normal. This would indicate to me that the fan needs the electronics to vary the speed that it runs at including the start up check so therefore it is not the oil inside settling outside the central reservoir causing the fan to operate at start up.
Cheers,
Murray
Typically it’s close interference between the two halves (fan half and input half) like two coarse hair combs fitted together but not touching. The oil when present causes the grip without any mechanical connection. Its on or off.
To get variability is more like a wet clutch on a motorbike or the Transfer Case with all associated oil fouling, filtering and servicing needs.
So, I’m sceptical it’s anything more than an electronic over ride feature.
Only theorizing hear but maybe it's like active type shock absorbers that you can adjust the dampening while driving. I believe they change it electro magnetically. Don't really know how they work but I believe they is some sort of magnetic material suspended in the oil of the shocks that when you pass a current through it, it changes the viscosity anywhere from very fluid to locked up solid. This type of system would work for the fan.
https://www.haydenauto.com/media/567...ts_6980012.pdf
Pretty good read on how they work and vary the speed
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