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All I can tell you is that one esteemed company told me to fit the electric fan in front of the rad but this didn't seem as effective as I expected or hoped. I suppose the position of the fan in front provided a little protection from stones hitting the radiator. But when the fan is not running then it partly obscures the natural flow of air through the matrix so possibly promotes heating until the stat operates to switch the fan on.

I will try a puller fan (not suck please!) Revotec has been mentioned but I'll look at others to see what their CFM's are.

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Pullers are reportedly a little more efficient, but there are often more space constraints on the backside of the radiator.  I believe either position can work fine if you choose the right fan.

Ed

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1 hour ago, Drewmotty said:

Sucker every time. It won’t obstruct or disturb airflow through the matrix so cooling will be more efficient especially when underway. That way the fan won’t have to run so often. 

I installed a pusher in front of my rad over the summer with a manual switch. I also have the engine fan.  I expected the temperature gauge to increase a little because of the perceived obstruction (the pusher fan) in front of the rad.  In reality i didn’t notice any difference in the car running slightly hotter. 

 

In my simplistic world, as long as you are moving then you have all the air flow you need through the rad to cool the engine. I installed mine for the occasion when you are stationary in traffic on a hot day (continental driving) where you can switch it on manually to increase the air flow. 

 

The conclusion I drew was that push or pull, with or without engine fan, doesn’t really matter because as Ed says, if you chose the right fan then it will work fine. 

 

Cheers

 

dave

 

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Paul,

when selecting a fan, the flow rate (CFM)  number alone is not enough. You need to compare the curve that shows flow against (differential) pressure.

The radiator core is a restriction to flow.

buying the biggest diameter you can fit is a good thing too.

Waldi

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Paul

if you decide to use the through radiator fixing method (I did) use these felt pads eitherside next to the rad core on each tie. They help prevent movement/vibration and wear 

https://www.diy.com/departments/b-q-black-felt-pad-pack-of-80/1725349_BQ.prd

H

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With regard to obstructing airflow through the rad I can't see that it matters whether it is in front or behind because the fan sits right up against the face of the radiator.  Either way the body of the fan will be in the airflow and blocking it when it isn't switched on.

My fan is in front of the rad (pushing) simply because I bought the fan on ebay and it happened to be a pusher.  The fan is the biggest I could realistically fit and only comes on in traffic at which point it cools things down toot sweet.

Rgds Ian

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I have the full sized Revotec behind the rad, works just fine even stuck in traffic on the hottest day last year it kept the temperature under control. One thing is to make certain that the rest of the system is clean!

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The fan front or back of radiator fitment is always an ongoing argument, however it's long been accepted that the body of the fan PLUS the surface area of the fan blades (even though they rotate when in the airflow they slow and stall airflow) blocks off maybe as much as 25% of the radiator core PLUS it causes turbulence from the air it deflects which in turn slows down the passage of air through the rad core, increasing the loss of coolant affect.

The alternate fit of rear of radiator fan obviously has no initial blocking affect upon airflow allowing 100% of surface area to be accessed by incoming air , the rear of rad fan causes a reduction in cooling effect because of the fan motor body blocks the airflow over it's surface  area and the slowly rotating fan blades in the airflow causes a stalling effect (slowing the airflow). However the losses caused by these affects are less than the aforementioned front fitments because the air has at least cooled the core whilst passing through it and the rotating fan blades even when not powered allows air flow which even though slower has a cooling affect and a reduced effect in the stalling of the airflow.

On cars of a more modern design ram effect air cooling from the forward motion is often very restricted (think of Minis and the like) and they depend upon the radiator being a heat sink and the fitted fan pushing or dragging the air through the rad which cools sufficiently as long as the heated air can be got away from the rad area.

Mick Richards 

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Cor(e) blimey,

             I would have thought somebody would have jumped on the thermodynamics in quick order by now. But alas no.

With the fan in front the cold (thicker air) has more difficulty squeezing around the blades etc than the warm thinner air (having gone through the core).

The warm thinner air will easily, yes easily I say, flow around the blades.

However this is contrary to nature as most of nature pushes. Have you ever tried pulling a snooker ball with a cue.

Mind you have you ever tried pushing string.

 

Nurse - why ????

 

Roger

 

 

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Well the density of air reduces by about 18% from 15C to 80C so there is an effect there which may affect cooling by a couple of %.  On the other hand  the thinner hot air will reduce the efficiency of the fan behind the radiator when its running so that has to be taken into account too.

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For my damper project, I needed an electric fan for the rig.   A visit to my local breaker found that a TRansit (!) van fan is just the right size and comes in a plastic housing that can be cut down to hold it in place.  And it has two speeds!.   Cost?  £10.

John

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But the volume of air will expand  by 15% as it heats up in the core. So velocity has to be faster around a sucker's blades, meaning the fan will flow less air mass of air per second.

But that said I doubt it matters, fit it where its easiest or looks best.

Peter

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A fan in front, grill side, of the rad is more likely to free wheel due to the air flow. The speed it reaches can exceed the bearing ratings and shorten there life. The question is could you use the power the fan generates free wheeling to charge the battery and to control it's speed!

Mounting the fan the engine side should reduce the free wheeling speed as it's behind the rad.

Dave

 

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"The speed it reaches can exceed the bearing ratings and shorten there life"

I'm not convinced about that given the normal running speed of the fan but If it worries you, the fan can be electrically braked by connecting a low value resistance across its feed when it is unpowered. The resistor may get quite hot so needs to be suitably rated. The lower the resistance the greater the braking effect but don't go so low that the current exceeds the motor rating.

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This is my theory.

When driving there is a lot more air trying to get throudh the grille than can actually get through the rad leading to a higher pressure in front of the rad than behind it.

Even if the flow through the rad is only 5mph (88inch/sec) then the air is only in the core for about 0.02 sec. I doubt if the temperature rise of the air is anything like ambient to 80C in 0.02 sec. & the change in density is insignificant.

As long as the fan cowl (frame) is close to the rad it doesn't make any difference to the speed of freewheeling as the speed of the air ging into the rad will be about the same as the speed of the air coming out.

At the end of the day you pay your money & make your choice. It doesn't really matter.

I have a pusher & it gives a little more room when turning the engine over on the crank bolt to set the tappets etc. Otherwise I would't worry about where to put it.

:ph34r::ph34r:

Ready to be shot down in flames

Dave

 

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The majority of manufactures of modern cars have the fan behind the radiator ( assuming they have all done their homework )

this would appear to be the most effective position.

 

                                                      Harvey S. Maitland

 

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1 hour ago, RobH said:

"The speed it reaches can exceed the bearing ratings and shorten there life"

I'm not convinced about that given the normal running speed of the fan but If it worries you, the fan can be electrically braked by connecting a low value resistance across its feed when it is unpowered. The resistor may get quite hot so needs to be suitably rated. The lower the resistance the greater the braking effect but don't go so low that the current exceeds the motor rating.

Rob, It would be better to use the power to charge the battery, than dissipating it as heat in a resistor. Hence the suggestion.

The free wheeling of the electric fan is a factor considered by the present day motor manufacturers. Both as a source of power and bearing speed limits.

Dave

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17 minutes ago, DaveR said:

Rob, It would be better to use the power to charge the battery, than dissipating it as heat in a resistor. Hence the suggestion.

The free wheeling of the electric fan is a factor considered by the present day motor manufacturers. Both as a source of power and bearing speed limits.

Dave

Would the output voltage of the rad fan be high enough to charge the battery !!

 

Roger

 

Ps - amazing what effect a tongue in cheek comment will have.  Thermodynamics !!!!:lol:

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A good idea perhaps on first sight but complicated to implement Dave.  The voltage coming from the fan will vary greatly with speed and you would need some sort of DC to DC converter which would accept that varying input and produce a meaningful steady regulated output suitable to charge the battery.  Such things do exist but you then need circuitry to switch it on only when the input reached an acceptable level. A further complication is that normally the battery is fully charged anyway from the dynamo or alternator so there may not be anywhere for the fan output to go.  You could of course provide it with its own battery to charge, separate from that of the car.

The next factor is that you don't get something for nothing and the energy taken from the fan to provide any charge must come from the energy developed by the engine to move the car. You would actually be adding slightly to air resistance, so since nothing is 100% efficient the energy 'saved' would be less than the extra energy expended. The only time you might get savings would be on the overrun when slowing down.

 

Edited by RobH
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Bob, as a fellow time served engineer I agree with your comments. But the eco car manufacturers are now using the brakes to provide charging power for the battery. I guess electronics are now cheap.

Dave

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