kenlowe, Pacet or Other Fan

[02GF74]

Offroading means using low gears and so slow forward speed, but engine can be under high revs and high load, therefore generating a lot of heat.

Low forward speed = low natural air flow through rad (NOT talking about engine speed here).

Just because the landrover itself is going slowly, doesn't mean engine isn't working hard.

Regards,

Diff

... but most of the time the engine would be running slowly otherwsie you would change down a gear rather than rev the b*lls off it surely? Once in a while you need to give some stick but that is the exception rather than the norm surely????? .... but still this noone has come up with an explanation to make me happy

[Mark90]

Without knowing the fan performance, it is difficult to tell.

Exactly.

I have found it very difficult to get figures for the amount of air (cfm) that various fans can shift, both electric and viscous, seems only Kenlowe/Pacet/et al publish figures. I've tried getting cfm figures for viscous fans or factory fit electric fans for various cars with no real success.

Arm waving and outlandish statements are all well and good but where the tech/figures to back it up?

All I can say for sure about my electric fan setup if they shift a lot of air (being electric they do this at any engine speed) and they 'seem' to shift more air than the viscous fan on my tdi, I reckon they are pulling over 2500cfm between them (2x12" fans), but it's very subjective and I can't really say for sure.

[simonr]

I'm not too keen on viscose fans (must remember to replace mine before France next week!) - they are not terribly reliable.

Electric fans have an advantage in terms of cost and controlability (and they are easy to bodge a replacement in an emergancy)

Although I'm still using viscose, I have installed the wiring harness for an electric 'just in case' fan.

I have read that an engine driven fan is capable of drawing 6hp from the engine a high speed. It would seem reasonable to assume you would need a 4.5kw electric fan to shift as much air.

However, engine fans are generally designed to run at low speeds and as the speed increases, the efficiency drops like a stone so it is possible that the fan spinning at 5000rpm is barely shifting more air than at 2000rpm.

One way or another, it seems that a typical 200w fan can shift sufficient air to provide the cooling you need. This is one of the major savings associated with going electric. The saving in power could easily be 5% of your engine output - most of which is being wasted as extra heat!

My Mag-clutch-fan should provide a best of both worlds solution to this - but it's still at the prototype stage (Mk3 being machined next week with a bit of luck!).

Si

[BogMonster]

It certainly cannot be saying that to move the same amount of air as a viscour, an electric fan needs to be 14 ft diameter - that has to be wrong as any plane buff can tell you.

It is not about power but shifting air.

Know of a lot of electric aeroplanes do you?

The Tdi viscous doesn't seem to do much simply because the engine doesn't produce much heat most of the time so it doesn't lock up. Leave my Discovery idling for a while after a long run on a hot day (4.0 V8 surrounded by lots of bonnet insulation and hot exhaust pipes) open the bonnet and blip the throttle to a couple of thousand revs and the viscous fan produces more wind than Hurricane Katrina! It only needs to run like this for about 10 sec and the rad is down to temp and it unlocks again. The vehicle also has electric fans fitted and when I had a faulty viscous unit they were running almost all the time to cope.

I'm not convinced about the power saving thing - if a viscous is unlocked it should be draining very little power (put the nut of the viscous unit in a vice and spin it till it unsticks, then it will spin fairly freely) and when you need cooling, directly using the mechanical energy to spin the fan must surely be more efficient than converting it to electrical energy and then back to mechanical again...? I am still running my Tdi without the viscous to try and persuade it to warm up quicker and it does seem to rev very slightly more freely when absolutely cold, but I don't know that there is much difference.