From: Impmann@aol.com
Date: Tue, 12 Jan 1999 16:32:29 EST
Subject: [imps] Re: Overheating/Rad Fans

Hello all,

I don't know if anyone has any experience of these, but years ago there used to be fans available for the Imp that had blades that varied their pitch in relation to the revs....

These are similar to the type used on some racing Minis; the idea being is that the greater the pitch the greater the cooling. Anyone ever used one, or even seen one??

For my money... if you are going to do away with the back fan, do away with the back radiator. If you don't want dingly-dangly pipes use the heater pipes like the Cashmores, along with a Sunbeam 930 water pump assembly (cheaper & neater in a front rad conversion). Use a Fiesta Mk1 rad (peanuts from the breakers) with it's electric fan. Don't bother with the thermo switch, as by the time the coolant is boiling in the rad, the engine's already cooked. Use a manual switch and a good temp gauge. You won't need to use ANY fan on the motorway...the faster you go, the cooler the rad. You'll only need the fan in traffic like any normal car, and put simply the car is more likely to underheat.... it's certainly the way I'm going with the Sunbeam Sport!!!!!!

Cheers,
Tim

From: Gary Henderson
Date: Wed, 13 Jan 1999 09:31:30 +1300
Subject: [imps] Re: Overheating

Hi Dave
Fair enough!
In view of no or little natural airflow, and also in view of concerns re bearing life and cavitation in the waterpump, perhaps a bigger waterpump pulley, smaller crankshaft pulley and a booster electric fan (for slow traffic and/or hard thrashing) might be a good compromise? (Just theorising - I haven't done it.)
The standard fan, with its stator blades in the cowl, can push against a bigger pressure head than most other vehicle fans.

How about a Holset viscous coupling, as used on Hunters etc? Anyone tried one? (It was worth about 2 hp to a Hunter, probably more for an Imp due to the stator-blades mentioned above.)

Cheers
GaryH

From: Mark Norman
Date: Wed, 13 Jan 1999 10:37:29 -0000
Subject: [imps] Re: Overheating/Rad Fans

I believe Jaguars & some Japanese cars in the 80's had a heat actuated clutch on the fan. These were about 6-8 inches diameter & 1.5inches thick. They would rotate freely when the radiator was no too hot, freeing up some engine power, then as the temperature rose, they would engage the fan. Given that the Imp fan has a fairly large central core, does anyone think it would be worth/possible trying one of these?
Alternatively could a centrifugal clutch be made, like the ones fitted to yo-yo's nowadays, that would allow some slip at high rev's? Or am I just rambling nonsensically?

mark

Date: Wed, 13 Jan 1999 11:38:58 -0000
From: Dave Edge
Subject: [imps] Re: Overheating/Rad Fans

I don't think that the heat related movement would provide much benefit other than during cold warmup drives, even then maybe it is better to make the engine work a little harder to warm up faster.

The issue of a centrifugal clutch sounds interesting though, I think that the mechanical fan is superb below about 3-4krpm. After that it becomes a power sucking nuisance. In the low ranges I even think it makes a nice noise. If you put two imps next to each other, one with an electric fan and one with a mechanial one. Just watch and listen to the difference in the way they both rev.

A heat engaged and speed limited fan sounds tempting, I would even consider going back to mechanical.

Do volvo do anything Nick?

Dave

From: Nickcleak@aol.com
Date: Wed, 13 Jan 1999 16:29:27 EST
Subject: [imps] fan power

> Imps fans consume a bit more than 2bhp more like 4 !

it's 7 @ 7000 rev/min isn't it ?? nick ...

From: Gary Henderson
Date: Thu, 14 Jan 1999 10:03:42 +1300
Subject: [imps] Re: Overheating/Rad Fans

Hi Dave

The old 'Feath'rin Fan' has appeal, because it is less likely to suffer from high-speed stall of the blades. But the blades themselves don't look that clean in an aerodynamic sense.

My Mitsi L300 4x4 has a Holset-clone viscous coupling.

Several Japs had an electric clutch for the fan, driven by a thermo switch.

The Japs seem to save pure-electric operation of the fan for east-west setups.

Don't agree with working engine harder to warm up faster - wait until the clearances have stabilised and the oil flows properly...

Cheers
GaryH

From: Nickcleak@aol.com
Date: Wed, 13 Jan 1999 17:56:50 EST
Subject: [imps] Re: Overheating/Rad Fans

Hi

> A heat engaged and speed limited fan sounds tempting
> Do volvo do anything Nick?

yes , they have had viscous fans from 1971 until 1993 when they decided in their wisdom with Air-conditioning Condensors, intercoolers , Oil coolers , power steering coolers and auto transmission oil coolers , that a nice big electric fan is required ... and BIG it is , 15" dia blades which suck your clothing into the grille if you are standing close when it cuts in !

The viscous fans had a course pitch fan blade that would move a lot of air at low rpm , then the resistance of the bladed through the air at higher rpm would cause the viscous hub to heat up and slip and the fan would free wheel ... They also had a bi-metal coil so that if the air coming at it through the radiator got too hot it would unwind and tighten up the clutch and more drive hence more air blown through ..

I feel the Imp needs all the air the fan can put through it though especially at high rpm ..
Another thought , make the radiator say 4 or 5 inches deeper and angle it , you would have more surface area from which to get rid of the heat .. rather like single seater racing cars who have a tiny radiator set at about 10 degrees from the horizontal ...

Nick

From: Nickcleak@aol.com
Date: Fri, 15 Jan 1999 14:06:01 EST
Subject: [imps] Re: Overheating/Rad Fans

> 'Feath'rin Fan'

Trouble is , you want the airflow to still be fairly strong at high rpm not tail off ...as there is no natural flow, so this will not work on an Imp..
The idea of those fans which reduce the pitch of the blades as rpm increases was for a conventional car which had adequate airflow from the forward motion of the car , so would benefit from the less drag of the fan blades when on the move ...
Nick

From: Gary and Carol Henderson
Date: Sat, 16 Jan 1999 08:54:14 +-1300
Subject: [imps] Re: Overheating/Rad Fans

Hi Nick

My point is that at some speed, the standard fan will simply be too coarse in pitch to work properly; it will then spend most of its effort spinning a block of air around inside the cowl, with centrifugal action causing leakage off the tips, half of which will recirculate to the intake-side...

I can't document just what revs are needed to cause this to set in, but as Rootes would have gone for max achievable flow at lowish revs, for anything much over 6000 rpm a finer pitch would probably be an advantage in actual flow. I'm not so sure that the dogsbreakfast blade assemblies of the Feath'rin Fan could actually deliver this advantage! I think I'd rather slow the fan & waterpump by, say, 20%.

By the way, a source of electric-clutched pulleys: Dead automotive air-con compressors.

Cheers
GaryH

From: Nickcleak@aol.com
Date: Sat, 16 Jan 1999 05:01:53 EST
Subject: [imps] Re: Overheating/Rad Fans

> a source of electric-clutched pulleys: Dead automotive air-con
> compressors.

excellent idea .. but they all seem to have the Poly-vee grooves which need a belt that has to be tensioned very tight , the imp water pump wouldn't last 5 minutes ...
..
Nick

From: Gary and Carol Henderson
Date: Sun, 17 Jan 1999 00:07:02 +-1300
Subject: [imps] Re: Overheating/Rad Fans

Hi Nick

No, not like that! I meant as the basis of a latter-day Holset substitute in the fan hub.
At the other end, it would stop the water-pump.
They seem to be rather well-made units...

Cheers
GaryH