Soarer Central: Thermals

Soarer Central Mechanical - Common Thermals

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Hayden Miller
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Monday, December 04, 2006 - 09:37 pm, by: Hayden Miller (Zero)

Wow Mark, you sure have a lot of built up hate about E-fans.... is there something your not telling us, maybe a childhood accident involving an E-fan?
Were here for you, you can talk about it

Classic argument but some great info on both accounts

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Monday, December 04, 2006 - 09:40 pm, by: Mark Paddick (Sparks)

And I quote;

"Can you identify the greater inefficiencies in the latter setups which might allow an electric fan to be more efficient? " unquote

I can't and I did the Uni degree on the subject.

However, I have been thinking about it a lot lately as I have a car that won't be standard and won't be able to use either of the factory systems without a lot of mods.

The alloy radiator question is interesting as I've been thinking that way for a while.
Despite what I've said above there are cases where electric fans can be useful.

In all three examples I gave above (not just the old Corolla as accused) of factory designed systems NONE can be called fan cooled.
All are stand alone pump driven cooling systems that rely on vehicle movement to create airflow (which is NOT free power. It alters the drag coefficient of the vehicle and so costs fuel) and thermal mass of the radiator to smooth the peaks in heat production.
The electric fan is there to provide some airflow to help the radiator do that when the car is not moving but it can't cool the engine and if left standing with the engine running for long enough all three systems will boil despite any efforts of both electric fans in all cases except the Ferrari.
The Ferrari takes about an hour and a half but it will get there almost. It's oil cooling system can cool the engine enough to prevent this ever happening though so it will get hot but as soon as it moves it will settle back down.
Ferrari warn about doing this as it places undue thermal stress on the system and potentially increases engine wear. They suggest that after about twenty minutes or so that it would be a good idea pulling off the road and going for a quick meal or something until the traffic clears allowing the engine to cool a bit. They say you will appreciate the marvels of Ferrari engineering much better with a full tummy and a clear road.
One advertising claim that I have no problem with at all

This all comes back to the alloy radiator and would you believe that a lot of radiators specifically designed for this fan-assisted type of setup are alloy types.
Not surprising really as one of the prime requirements for this system is a large heat sink which is usually, but not always, in the form of the radiator. Thus the radiator has two main functions.
Alloy is quite a good, and more importantly cheap, material to make a heatsink from.
So if you put a dirty great alloy radiator in place of the factory one, preferably with fin design to suit but they're not all that different and any will work, you would end up with a system that may just be able to do the job nicely.
Hopefully the electric fans would only rarely be needed but this would depend on whether the heatsink affect of the alloy radiator was big enough.
I don't know for sure but I think it may work.
The key technical words in all that for it to work are "dirty great".
It would need to be pretty big but where just a normal radiator that only cools air does not gain much advantage by being thicker a heatsink does and since that's what we want the radiator can be made very thick (just like the Ferrari). The thin design of some fans will help here.
It's cooling effect due to air passing through it won't be all that much higher than a thin one BUT it will be a real good heatsink and THAT is what we want.

So in answer to your question "do you think if you had an aluminium radiator or something liek that, that thermals would be just as good"

Yes they can be just as good and possibly even better but it won't be the fans that do it it'll be the radiator and it will have to be a big bastard and that implies not too cheap.
And, yes if the radiator is good enough the whole efficiency of the system would be as good or better than standard. Given that the standard one is pretty damn good even a large increase isn't going to be much but it will be at least as good as most of the cooling will be done by direct conversion of the cars' motion.

Once the radiator becomes too small as a heatsink it can no longer spread the thermal load and the fans have to work flat out all the time and efficiency is blown away. So ideally the best system has no fan at all and the Ferrari is very close to that.
This of course disregards any effect the total weight of the different systems may have on the cars' performance but it will be relatively minor.

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Monday, December 04, 2006 - 10:04 pm, by: Mark Paddick (Sparks)

No not E-fans, Hayden.
But I do really have a very big dislike of overheated engines and the two do tend to go hand in hand.
An electric fan cannot cool an engine and cannot replace a well designed clutch fan if that is all that is done which is what I said in the first place.
Nobody ever asked me if they could work, and they can, until Nathan's alloy radiator question which was really a very good one.

I have been involved in a lot of motorsport over the years and every time an electric fan appeared on an engine it was trouble.
I put this down mainly to the manufacturers who spend so much time trying to prove the things are good they forget to tell you that you must have a heatsink in the system to spread the load.
This means the fans don't have to cope with the heat peaks from the engine; they can take their time to cool the radiator at a slower, longer rate.
The bigger the heatsink the less need for fans and I think the manufacturers are frightened you will twig to that and won't buy any more fans.
They're wrong. Even the Ferrari which has no need whatsoever has a couple of fans tacked on for insurance. All designers of any sort would take that option for extra insurance in any design in any field unless they had a really good reason not too. Cost will usually do it but that is a bean-counters' decision not the designers'.

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Monday, December 04, 2006 - 10:30 pm, by: Mark Paddick (Sparks)

Oh and as for electric fans being shrouded, they are but the shroud needs to cover the whole radiator surface area and the shroud on the fan only does the fan.

It's easy to make a shroud. That is definitely not rocket science and is somewhat surprising in light of the effect they have.
Simply make a flat panel of, say 1/8th or 3mm plastic sheet (corflute will do for experimentation but isn't really strong enough for long-term use) that is a bit smaller all round than the radiator and space it out using sloping pieces of the same stuff.
Now cut holes in the shroud for the fans. The idea is that all air goes through the fans and there are no gaps between the shroud and the radiator and/or fans.
Ideally you should work out the spacing of the fans from the core and so the size of the sloping panels but practical considerations get in the way of that and is doesn't affect the outcome that greatly anyway.
You don't want the fans too close to the core or the airflow will be lees straight than it could be for the edges of the core. This is a simple explanation to enable making the shroud. The real thing would take me all night and I've had enough for a while.

I will be back to prove how increased load above the "maintenance" current of an alternator absolutely MUST increase the wear on all moving parts of the alternator and reduce its' operational life expectancy. This is not a square law relationship but is in fact a cubed law which means that for each increase of current above the maintenance threshold the wear factor will be cubed. ie. double the current and you increase the wear 8 times. Treble it and you increase the wear 27 times.

Yes, Nathan, your battery and alternator may have survived the punishment so far but I guarantee they're worn out.

If I were writing a report now is the time I would go and look for a fully qualified Auto Electrician with at least several years experience rebuilding alternators and an understanding of how they work and what causes the problems he is fixing every day.
But since I am one (although I choose no longer to practice the trade) I don't feel the need.

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Monday, December 04, 2006 - 11:01 pm, by: Rehan Bandara (Parsec)

Most of your reasoning is sound, but i'm a bit dubious of your wear cubic law.

It's safe to say that for the most part a doubling in the current drawn from the alternator doubles the opposing torque the alternator puts on the serpentine belt, so we can say that the radial force on the bearings is doubled. I don't know how many bearings are in the alternator, but i'm guessing there are one or two. If there are two, the increased radial force on the bearings can be shared, depending on the design of the shaft and housing.

So there's double the force on the bearing's outer race, and double the peak force on the rolling elements and inner race.

I think saying that a doubling in the radial force increases the wear 8 times is an oversimplification. I think it depends a lot on the lubrication, material, bearing design and rolling element velocities.

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Tuesday, December 05, 2006 - 01:34 am, by: Mark Paddick (Sparks)

Yes that's right. From a purely mechanical point of view but there is more.
I must admit I wasn't really considering the mechanical loads on the bearings and such but even that relationship will tend towards exponential as the other mainly electrical causes decrease the efficiency of the alternator increasing the required force per unit output power.
The cubed bit doesn't apply to the mechanical loading but it does to the brushes in particular and output current carrying conductors subject to friction. Slip rings in some designs but there are other ways. All will have some form of contact carrying the current.
This is because there is more than one force causing the wear. Mechanical friction and heat, electrical friction and heat are the two main causes but the two heat components add exponentially. And each is self perpetuating, more heat generates more friction, more friction generates more heat and the same for electrical conductance, more heat = less conductance, less conductance = more heat.
On top of that there are two more heat sources and one increases exponentially with output current.
Heat from the engine and heat from the diode rectifiers used to rectify the usual 3 phase output of the alternator. It's not exactly a cubed law but that'll do for a quick summary.
The whole thing contains somewhere in the order of 15 to 20 terms from memory.
The real point is that it isn't a linear equation and depending where you look on the curve it can be described many ways. Probably a better way to describe it would be;
If you increase the load current the alternator will fail sooner and the more current the worse it gets and this tends to be an exponential relationship.

As for the rectifier diodes the relationship between current and mean-time-between-failure starts a straight line at low currents and is around 45deg., but as the current increases the curve steepens and ends up vertical, and this happens a bit BELOW the rated output current of the diode.
The heat generated by the diodes is transmitted directly into the alternator housing, so it can't be gotten rid of easily like the engine heat which can be shielded. Again this is an exponential curve until the diode reaches the current and therefore temperature which will melt it.
This is why they are never soldered but connected with crimps as at high loads (a constant load UNDER the rated output is enough) the diodes get hot enough to melt the solder (it only has to soften it slightly and current and heat in the solder do the rest along with a bit of help from vibration.).

All of this heat also heats up the wires in the various windings of coils within the alternator and their own current caused heat adds to it.
This apart from anything else can cause the windings to expand. If they don't come into contact with something not doing the same speed they will eventually fracture from heat stress and the more output current the more likely that is.
Even if you only look at the heating effects of rising output current on the structure of the case it is the same. Heat stress will eventually crack it. More output current is more heat stress.

All conductors in the alternator will experience a rise in resistance due to heat and that decreases the efficiency and the mechanical force required to generate a given amount of power increases along with it.
The voltage drop across the diodes increases with current and heat reducing efficiency with a repeat of the above increase in mechanical force as the consequence.
It goes on and on and some of the effects are small but others are not. They all add together.

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Tuesday, December 05, 2006 - 01:50 am, by: Mark Paddick (Sparks)

Fortunately for me this becomes something of a non-problem for my car as a large alloy radiator will hopefully be capable of doing the job without fans anyway so any fans that are there won't run too long.
And the new engine has a larger alternator than the old anyway.

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Tuesday, December 05, 2006 - 01:51 am, by: Rehan Bandara (Parsec)

ah yes, good point, i didn't consider the brushes or other electrical components.

I think you meant to say more heat = less resistance. (conductance being the opposite of resistance). Also, you mentioned in the last paragraph that resistance rises due to heat. I was under the impression that in most metallic conductors it falls with increased heat.

I'd be interested to see the functional equation describing the wear and failure of alternators.

Intuitively I'd say the diodes aren't much of a worry, but brush wear and arcing could definatley be cubic.

I was under the impression that modern alternators are brushless, but i could be entirely wrong about that.

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Tuesday, December 05, 2006 - 01:57 am, by: Rehan Bandara (Parsec)

I always wondered whether you could increase the power to weight ratio of alternators by opting for plastic insulation in the windings instead of enamelled copper windings. By then using less windings (as the insulated wire takes up more space), the alternator is run at much higher speeds to compensate and to create very high voltages.

Do you think this is possible? I know the prius' electrics run at 32kv, so i'm guessing this is their closely guarded secret to high power to weight ratio alternators and motors.

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Tuesday, December 05, 2006 - 02:06 am, by: Mark Paddick (Sparks)

No I got it right more heat = less conductance = more resistance, resistance is the inverse of conductance but I confused myself too by changing terms for resistance and conductance as I reminded myself that conductance is the real term to use and then thought it'd be funny to see who picked up on it.

I had to write that out three times before I got it right originally.

There can be several ways of looking at it but I always remember the analogy of electrons around atoms. The more energy they have the harder they are to get to change direction and heat gives them energy.
There is another effect where the electron is lower down the valence level and harder to shift away from the nucleus but that doesn't apply here once the temp is up above freezing as all the electrons will have enough energy to be in the upper valence levels.
There's a whole lot of other effects too but the biggie is the diodes anyway and they always increase their losses with heat and current.
It is diode failure that will kill an overloaded alternator first in most cases so all the other stuff is really incidental but it was fun dredging some of that up just to see how much I could remember. Not that much unfortunately but enough I reckon.

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Tuesday, December 05, 2006 - 02:26 am, by: Rehan Bandara (Parsec)

Ah yeah, you're right about that one. more heat = more resistance. Your mind games are confusing me

That raises and interesting point that i glossed over actually, as it means that for a given amount of current, a lot more heat is dissipated in the alternator. Initially I was thinking in terms of the amount of power the alternator generates, but if you think in terms of current, the alternator has to supply more power simply to overcome that increase in resistance to generate more current.

You are on the right track in visualising electron energy levels... however you've missed a few key points.

The reason why the resistance increases is because there is a higher statistical probability of inter electron collisions with larger electron kinetic energies (which are random due to heat, but somewhat ordered and directional when a potential difference is applied, insert many second law analogies). Einstein called this the "drunkards walk"

Copper or any other metal will form an ionic lattice of positively charged nuclei and an electron "gas". The electrons in the gas define the intrinsic energy that the conductor possesses based on the "fermi dirac" distribution, which is dissimilar to the simpler energy bands and discretisation found in atoms (valence levels)

I think we've killed the thread without even going into diode IV characteristics. The same applies, however the situation is more complicated due to the bandgap formed by doping (purposeful impurities) in the ionic lattice.

From memory this means that increasing the temperature can dramatically reduce the resistance, and then increase it as the upper band fills. I remember gallium's conductance peaks somewhere slight above room temperature.

Do you have an electrical engineering background?

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Tuesday, December 05, 2006 - 02:50 am, by: Mark Paddick (Sparks)

There've been some interesting experiments done using a mixed alloy wire that's very thick and so not a lot of turns, low voltage and huge output currents. I'm not sure what the insulation was but it would have to be good because they used liquid Helium to cool it to superconductor territory. Losses were totally small to non-existant in comparison and efficiency astounding if the Helium cooling is ignored. Not too shabby with it either but I can't remember the figures.

This is basically the opposite way to do it but they did show that it works. It'd be a long way off yet though.
The high voltage approach has been talked about for years a probably should have happened ages ago but it's like 12V inertia. Once it starts the change will be rapid because it will definitely work and work now. No development is needed.
By increasing the voltage the current is proportionally reduced and it's the current that's the big bad nasty. The voltage/curent relationship may be linear but the heat and resistance effects are not.
Just a simple application of Ohms' law will do here anyway;
E = I x R where in this case we are looking at the voltage drop across a current carrying conductor which is our power feed.
The resistance of the wire can be regarded as constant here as we're not talking about overloading just normal operation.
For every decrease in current the voltage drop decreases and so do our losses. This gets even better because as the voltage of the supply goes up and current down the percentage of the total voltage of that voltage drop decreases too.
There are other considerations but none that detract much from the outcome.

This approach has been proven to work in power distribution systems and has been used here for years in our grid network. All long distance distribution is high voltage / low current because the losses are so much smaller. It only comes down to 240v when it gets close to the end user and doesn't always come down then.
Even the added expense of all those transformers, and they are a large percentage of the cost and they're not cheap, doesn't detract enough to render it uneconomical. The savings are so great.
The extra cost are partially offset anyway; increased voltage allows smaller distribution conductors and there can be quite a saving in copper even though some must go to the transformer construction.

It's better to change the winding ratio and keep the speed down as the mechanical frictional losses will increase exponentially with speed but the result is the same. And lower current allows thinner wire which allows more turns which increases voltage which is all bloody good really.

Going to higher voltages again as you suggest may work too. The problems will come when the voltage is high enough to start breaking down normal insulations. Initially at least even increased friction can be ignored and there are always improvements in techniques and materials there too anyway.

At this stage it looks like at least Europe will settle on a 40v or thereabouts automotive standard. all the experts reckon they should go higher but there's some reason they don't want to that I forget. It didn't make much sense to me which is probably why.

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Tuesday, December 05, 2006 - 03:02 am, by: Rehan Bandara (Parsec)

Frictional losses don't nescessarily have to increase. There is no particular reason to have any mechanical coupling between the stator magnets and windings. Windage may be a concern, but in the context of some of the ridiculous engineering feats in modern cars, vacuum sealed alternators aren't far off the cards.

Superconducting is cheating. Until we find a room temperature superconductor (or crack fusion, whichever comes first), we have to make do.

both a higher speed and more windings result in a higher voltage, right? Let's assume that there are no mechanical losses involved. Do you think it's possible to create a very high power to weight ratio alternator that uses plastic insulation instead of enamelled wire? The assumption is that the windings are sparse and spaced out, and the rotor is run at ridiculous speeds off a turbine (like a turbocharger).

I'm thinking that as long as the wire is thick to support decent currents, and insulated enough to prevent high voltage discharge or breakdown, the only limit to the amount of power created is the torque developed by the turbine at speed.

It's easy enough to do for motors as the amount of poles can be increased and the windings can be incorporated into transformers in the whole assembly. I know ABB do this sort of thing.

I've been telling people for ages that its stupid that cars run on 12V. Nice to know that you (and all of europe) agree with me.

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Tuesday, December 05, 2006 - 03:09 am, by: Mark Paddick (Sparks)

And yes I've got quite a varied background but Electronics engineering is part of it along with some thermal engineering and flow mechanics (mostly related to engine flow rates). A couple of apprentceships too, one in Auto elctrics and one in Radio/TV.
Electronics design and maintenance for research schools at Uni's and stuff was the latest stretch of about 5 years. Thats the best fun I've had working I think and the facilities were fantastic. I got a lot of stuff I'd put off for years done.
A lot of the Uni work was thermal control related, keeping experimental gear within defined temperature ranges. (the young trainee there had a turbo Commodore V6 that we practiced some theory on and proved the total ineffectiveness of electric fans as an enginer cooler without a heatsink and learn't a lot about heatsinks too)
A lot of it is related to Electronics specifically rather than general engineering but I also spent a long while with Telstra and short ones with every other 'phone company. Mostly split betwen high frequency radio communications and battery and power supply and solar energy stuff there which may seem incongruous but actually makes sense as I spent a feww years building remote Microwave repeater siteswith my crew doing everything from ptiing the building on site to building the battery banks and either mains or solar power supplies to installing,testing, repairing and testing again 'til it met spec the radio repeater from scratch.
These days they just plonk 'em down plug 'em in and if the green light comes on walkj away which is why the Australian public will end up with the 'phone system they deserve (crap).
One of the problems with having such a wide range is I can't remember half of any of it now.

Basically the whole debate here could've ended with the more current = more resistance = more heat = more losses statement in the first place but that wouldn't have been any fun at all

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Tuesday, December 05, 2006 - 03:28 am, by: Mark Paddick (Sparks)

And, yes I do own all three (possibly 4 but I can't be bothered checking) cars used as examples.
Only one is currently registered and going though.

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Tuesday, December 05, 2006 - 04:36 am, by: Mark Paddick (Sparks)

Actually the Ferrari was the one that got me started on the higher voltage.
Unlike our current Toyotas they are mongrel damn things to start. Heaps of ignition current in twin systems didn't help either.
If the battery was good enough to spin it you could bet it wouldn't spark.
I gave up and did only the 2nd mod on that car of 3 that ever got done (like Soarers the headlights got attacked first 'cos they were horrible nasty sealed beam things). It got converted to 24v and never looked back. Always started first time and one click of the switch would spin it over about five times.
Of course that would've been better if there was always a spark so the whole lot got ripped out and a custom electronic ignition system put in with individual coil packs and all and computer control.
Everyone wanted to know when the fuel injection was coming but ripping those lovely Webers off would've been heresy at best.
That sorted the old girl.

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Tuesday, December 05, 2006 - 07:42 am, by: Matthew Sharpe (Madmatt)

If its still of any interest, I used to have a 1974 Triumph Dolomite Sprint, heavily modified, producing about 200 RWHP that the prior owner had fitted a large, high performance thermostatic electric fan mounted directly to the original radiator core.

The car would regularly overheat despite the fans best efforts. Also I would often note the engine idle would drop significantly when the fan was running, which was most of the time.

I eventually replaced the original viscous fan and shrouding that came with the car, and hey presto, no more overheating problems.

When the engine was rebuilt I opted to re-core the radiator with a modern style core suited to the electric fan, and once again fitted it. This worked just as well, though the electric fan was always noisy, and with hind sight I wouldn't have bothered.

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Tuesday, December 05, 2006 - 09:45 am, by: Mark Paddick (Sparks)

Exactly the point. To quote my first post in this thread;

" Easy. Best solution for a Soarer is NOT to even think about electric fans.
Do a search and you'll find out why.
Do not waste your time or money.

Yes, there are many cars that use them from the factory. Their radiators and cooling systems are designed for it. The Soarer ones are not.

A good way to kill a Toyota engine (and most others) is to run it too hot and/or let the temps vary over too wide a range (thermal stress). Electric thermo fans will achieve that nicely."

Unquote.

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Tuesday, December 05, 2006 - 01:33 pm, by: Braden Murdoch (Ribfeast)

Does anyone make a bigger aftermarket 1JZ alternator? I've looked everywhere and can't find one

I run electric fans on my 1JZ cressy, as the stock hydro pump failed and a replacement was $1100+. No overheating problems so far, varies by 5 deg C tops. Even when the old radiator was 50% clogged. I'd love to make up a shroud for them though.

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Tuesday, December 05, 2006 - 02:36 pm, by: Mark Paddick (Sparks)

some of the later models will have. Try the one for the VVTi engine or a Chaser or something.
There's bound to be one somewhere in the Toyota range that is bigger and will fit or can be persuaded to do so.
My VVTi V8 has a bigger alternator so I'm right

and I think I may have talked myself into a nice big alloy radiator. What fans will depend what fits, probably electric. It won't need much anyway and that is the whole point of designing a system FOR use with electric fans. I probably won't need the bigger alternator but it's staying.

It'd be worth checking with someone who knows if there's a core that will work better in the Soarer radiator. Sooner or later they all need one.
My old one is OK but I wouldn't go to all the hassle of putting it back in a car, with all that nice red stuff and not put a new core in it. It's 15 years old after all.
It won't be as good as a purpose designed alloy one but any improvement is worth the effort in this area I reckon. It's unlikely to make the situation worse and might just be enough to cut down on the fan run time which is really what you want.

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Wednesday, May 06, 2009 - 11:57 pm, by: Camron Garcia (Killacam)

what type of fans do high hp street cars run? and why?
Supras for example.

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Thursday, May 07, 2009 - 08:53 am, by: David Vaughan (Davidv)

quote:
Run [electric fans] normally on the street and perhaps 80% are alright. See track time or push it frequently, and watch the gauge climb. No efan setup works overly well on our cars. If proof is required, look at MKIV owners who race the cars. Everyone that ever went efan switched back after ONE day.

As Mark Paddick explained at great length earlier in this thread, high performance cars have high performance radiators, not electric fans on the same radiator.

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