which size fan

On or around Tue, 25 May 2004 21:22:10 +0200, "Gromit" enlightened us thusly:

by "hot" do you mean "at normal operating temperature", or "overheating"?

if the former, the fan should only be idling. when the temp goes up, it should engage.

interested to note that the one on the new toy is working - initially, when you rev the engine, the fan makes a big row, but after about 30 seconds it slows down to idling speed. haven't got it hot enough yet to see if it cuts back in, mind... The similar one on the Ford does the same trick, slows down after an initial spin-up, and it did once while tuning the gas system (3000 rpm stationary) get hot enough that it span up again.

Hello, Austin!

Piglet's viscous is like that. First thing in the morning he makes much noise ;-) However a rev to 3000 rpm for a few seconds will sort it.

both - the fan has never engaged at any temperature.

Conversly, the most resistance the fan VC offers is when it had been parked up in the snow overnight! Very useful :-)

Normal running temp is about 1/3 on the temp gauge, or up to 1/2 on a sustained run on the motorway. Once climbing, the temp will increase past 1/2 after a while and I'll stop and let it cool. The temperature rise can be slowed by having the cab heater on full blast, so I've come to the conclusion that when climing at medium revs at low speed, say 25-30mph in 2nd/3rd gear, there's insufficient airflow through the radiator hence supporting the conclusion that the fan VC is dead! This isn't helped by the fact that after 180k miles, it doesn't go up hills too quickly! Have I missed any other possibilities?

Not having seen a working one(!) I wonder is the magic fluid heating up due to internal friction when you rev it, thereby causing it to lock initially. Once the engine and fan speeds equalise, there's less frictional heat and it disengages. Isn't this how the diff lock on a disco works? Just guessing - feel free to flame ;-)

cheers, Gromit

On or around 26 May 2004 02:40:39 -0700, snipped-for-privacy@allstate.com (Gromit) enlightened us thusly:

ah well, 's probably buggered then. had a look at mine, and while it slows down, it ain't sufficiently easy to stop as I'd like to put me finger in there.

not really, presuming that your radiator is in good nick, and not blocked internally or externally. The V8 in the 110 used to overheat all the time, but a new rad miraculously cured it.

might be. I've only seen 2 that work meself. mostly, they seem to err on the side of spinning all the time, but I have heard of ones that don't engage.

quick cheapo fix is to fix the hub to the fan so it's solid...

Diff lock on a Disco is *not* viscous. Just one type of RR......

On or around Wed, 26 May 2004 13:07:10 +0000 (UTC), "Neil Brownlee" enlightened us thusly:

and the viscous coupling is not really the same as the one in the fan, either. the stuff in the viscous drive is such that it stiffens when subjected to a certain level of shear - you can make your own to play with: get some cornflour, and add a very little cold water, stir it very slowly, till you have summat like the consistency of golden syrup. this will flow, slowly. stir it fast and it grabs the spoon. grab it quickly with yer fingers and you can pick it up, and all the time you keep moving it, hold onto it. if you stop applying force to it, it goes back to semi-liquid.

's the opposite of thixotropic, I think.

The stuff in the viscous cooling fans responds to temperature, and gets stiff above a certain heat.

You're right. Something about pressure changing the material from liquid-continuous to solid-continuous.

30 years ago I even knew the right word for it.

Dilantant

P.

so what do you think if this piece of kit, or does anyone have experience of it?

It's Famous Four's own fan kit. I'm liking the rather substantial inline thermostat fitting which seems an improvement on kenlowe's capillary system which has caused grief for a few people.

G

Thank you. Very cogent explanation. (That's not the word I remember, though. I could pronounce that one.)

Just an update on my dead fan for anyone googling for information.

How to lock the cooling fan viscous coupling.

From the front of the VC, drill a hole through the VC unit from front to back, about 1 1/2 inches from the centre of the hub on the slightly raised area. Lock the hub using a suitably hardened peice of steel through the hole and secure. Note that a brass wood screw will NOT work for more than a few miles! The shear forces are pretty strong! (i didn't have anything else to hand)

If you are in the wilds and don't have a drill, its possible to make a hole with a suitably pointy punch and loads of landrover tool number 1 :->

Once you've holded the VC unit, it will throw it's magic fluid all over the place when running but doesn't end up on the fan belt so should a problem.

I also cut a 10mm x 30mm section out of the plastic fan, between 2 fan blades to allow me to get a normal sized 32mm spanner in to the securing nut for the VC. This may affect the structural integrity of the fan but I'm binning it soon so am not too woried. It hasn't fallen apart in the last 5 days.

Gromit