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Author: Subject: Cooling fan - in front or behind radiator
cosmicicecreamman

posted on 21/3/21 at 01:41 PM Reply With Quote
Cooling fan - in front or behind radiator

Gents,

I'm sure this has been covered before, but does anyone know if moving a fan from in front of a radiator to behind a radiator will make any improvements in cooling?

I currently have the fan on my Riot in front of the radiator. The actual fan works very efficiently when stationary for reducing the temperatures, but I was wondering if it being behind the radiator would improve the efficiency of the cooling system when moving.

Thanks

Stephen

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40inches

posted on 21/3/21 at 02:33 PM Reply With Quote
I did the opposite, moved from behind to the front and reversed the polarity, worked as good as
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Mr Whippy

posted on 21/3/21 at 03:16 PM Reply With Quote
Really I think when the car is moving, the fan will be happily spinning away regardless of whether its switched on or not so its going to make no difference.
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02GF74

posted on 21/3/21 at 05:34 PM Reply With Quote
This has been discussed before and as you can expect there are 2 camps: front and behind.

My view, and this is based on a friend who (annoyingly) beyond smart, is to fit the fan in front as the fan can push more than 1 atmosphere of air whereas behind it can never suck more than 1 atmosphere (vacuum).

Even with a cowl, which you should have to ensure all air goes through the radiator, the difference between in front vs behind is negligible as the obstruction of the fan and cowl is the same whichever way the air is being forced.

You can also take a look at production cars and both positions have been used altough nowadays behind is more popular due to packaging.

With the correctly sized radiator and thermostat fitted, you should not have issues when moving. If when stationary on hot days the fan manages to keep engine temps within limits, then you need not do anything other than fit a cowl and ensure the hot air is able to leave the engine bay, usualy via louvres in the bonnent.

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steve m

posted on 21/3/21 at 05:55 PM Reply With Quote
My kit cars have all had the fan behind the rad, as for me, i prefer the unclutted look when viewing the front of the car

some cars there isnt enough room behind the rad, and a friends 7 ltr cobra is one, you wouldnt even get a piece of paper between the rad and engine, so both fans are on the front

Most importantly, check the flow and rotation of the fan, as i must of been driving for a couple of years with the fan blowing forward through the rad





Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at




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cliftyhanger

posted on 21/3/21 at 06:22 PM Reply With Quote
quote:
Originally posted by 02GF74
This has been discussed before and as you can expect there are 2 camps: front and behind.

My view, and this is based on a friend who (annoyingly) beyond smart, is to fit the fan in front as the fan can push more than 1 atmosphere of air whereas behind it can never suck more than 1 atmosphere (vacuum).

Even with a cowl, which you should have to ensure all air goes through the radiator, the difference between in front vs behind is negligible as the obstruction of the fan and cowl is the same whichever way the air is being forced.

You can also take a look at production cars and both positions have been used altough nowadays behind is more popular due to packaging.

With the correctly sized radiator and thermostat fitted, you should not have issues when moving. If when stationary on hot days the fan manages to keep engine temps within limits, then you need not do anything other than fit a cowl and ensure the hot air is able to leave the engine bay, usualy via louvres in the bonnent.


I agree front or back should make no difference. However, with a cowl it will (I think)
In front the cowl will block airflow, and flaps will be difficult to open when the car is moving (though a louvre type should work). But if the cowl is behind, flaps are rather easier to get to work. I have used VW cowls on a couple of cars to great effect, one had flaps, the other little louvres to enable more air through when on the move

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coyoteboy

posted on 21/3/21 at 06:35 PM Reply With Quote
The most important thing is ensuring it is properly ducted and that if you're using a pusher fan, push with it. If you're using a puller, pull with it. Motors and blades are directional on all but the most basic fans.





Report your local potholes, it actually works!

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cosmicicecreamman

posted on 22/3/21 at 07:24 AM Reply With Quote
Thanks for all the replies.

The system works well at the moment with the fan in front of the radiator and from the responses it seems like there is no real benefit to either configuration.

Thanks

Stephen

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loggyboy

posted on 22/3/21 at 10:12 AM Reply With Quote
I've always taken the view for a car that gets hot on stand still you want it in front (as stated above regards to push being more efficent than suck), bit a car that wants the best cooling when on the move it should be behind as in front can block certain parts of the rad and diverts air before it reaches the rad, behind less so.
So it depends on the use of the car. On track or a B road blaster, you will be moving more than stopping. Used around town stopping/starting, or sat in a queue for a Hillclimb/autotest, you might want better stand still cooling.





Mistral Motorsport

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pigeondave

posted on 22/3/21 at 10:33 AM Reply With Quote
My one pulls and is on the back of the rad.
I used smoke pellets in a steel tube to introduce smoke to make sure the fan was working correctly (direction).

It was interesting to see where the fan was sucking air from when stationary. It appeared that engine bay air was being pulled around the corners of the rad and back through. I installed some ally sheets around the front of the rad to ensure that air could only be pulled from the outside.

This guy has done some good writeups on the subject
http://www.super7thheaven.co.uk/blog/cooling/

All round great blog through the whole build.

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Myke 2463

posted on 22/3/21 at 05:45 PM Reply With Quote
My brain tells me that anything in front of the radiator including fine mesh grill or fan reduces airflow. I have golf rad ( polo + 50mm wider ) and alloy panels between rad and nose cone with fan behind which only switches on when stationary for several minuets even when the zetec is driven in a spirited fashion.





Be Lucky Mike.

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tilly819

posted on 23/3/21 at 09:48 AM Reply With Quote
This came up when I was at Uni a few years back and we 'did the maths' to see.

We found it does not make a huge difference either way. But there is a SMALL efficiency gain from mounting the fan behind the radiator. You gain a lot more by implementing proper inflow and outflow ducting.

Don't think I have paperwork anymore but its just Bernoulli / flow rate / pipe loss and heat transfer equations if I remember correctly. Quite easy information for anyone to find online if anyone is really keen

Cheers





F20C Haynes roadster 440 BHP/Tonne www.youtube.com/handmadeextreme

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