Electric Fans - Suck or Blow

[Barrie]

I've always understood that it's better to mount electric fans behind a radiator to suck rather than in front to blow but I don't know what the science is behind it or the percentage improvement it provides.
Has anyone carried out experiments or is it published somewhere or is it just empirical?

[taximan]

Whenever debated the results are even, but refrigeration engineers swear by pull through.
Shaun.

[Steve Payne]

Think of air like water, have you ever tried pushing water up hill?

If you push air through a rad some will spill and go what ever way it wishes.

If you pull it through it all has to come through the rad.

Steve

[AH1951]

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[Barrie]

Thanks everyone for your replies.
Winco Payne's words were specially helpful in understanding what's actually going on.

I was hoping for a study which shows that suck pulls x amount of air through the radiator whilst blow is x minus etc. Perhaps a comment on the percentage increase by using curved blades as opposed to straight.
It would then help to decide whether it's worthwhile in terms of cost and performance to change from front mounted blower (non-Jensen)

[AH1951]

What's wrong exactly with your existing set-up?
Is it overheating?

[Barrie]

Not particularly but I've put a bit of strain on the cooling system by adding a/c.
Sometimes I have to 'nurse' the temp gauge if you know what I mean.
A control switch for the blowing fan is suspect so whilst I'm at it I was thinking of fitting a pair of Pacet suckers in place of the aforementioned Kenlowe.
There's plenty of room between the engine driven fan and the radiator and I was just looking for a bit of science to back up my ideas. I don't really want to remove the engine driven fan and go entirely electric.

[Steve Payne]

I don't really want to remove the engine driven fan and go entirely electric.

Why not? an engine driven fan flows hardly any air when you need it ( in traffic ) and saps as much as 15% of the engines power when you are driving at motorway speeds and it is not needed.

A pair of high powered fans and I mean high powered ( 450watts ) with proper control will keep any car cool as long as you have sufficient electric to keep then working properly.

Steve

[Barrie]

I don't really want to remove the engine driven fan and go entirely electric.

Why not? an engine driven fan flows hardly any air when you need it ( in traffic ) and saps as much as 15% of the engines power when you are driving at motorway speeds and it is not needed.

A pair of high powered fans and I mean high powered ( 450watts ) with proper control will keep any car cool as long as you have sufficient electric to keep then working properly.

Steve

Thanks Steve that helps to put things into perspective........
There is an alternator which was put on when a/c was fitted but I need to check on its output. I think it must be about 60 amps which is not great. (I don't know about Watts and how to convert if that's the appropriate expression.) the wiring is original (1959) and without a wizard auto-electrician I'm reluctant to change or update it.
Agreed about the awfulness of the existing fan but still reluctant to depend totally on electrics for cooling.
This is why I raised the first place because I'm seeking info and other people's views and experience.

[Chris_R]

Back in 1959 the norm was engine driven fans. Very few, if any, had electric fans. The new (1959) Mini with the radiator at the side of the car up against the wheel arch still had an engine driven fan.
Come forward to today and I doubt that a single car has an engine driven fan.
Engine fans were fitted because they were simple and cheap. Possibly electric fan motors were not so reliable back then, I don't know.
Once you are above about 30mph neither an engine fan nor any other kind of fan is needed, simple air flow provides enough throughput.
Us folks with Interceptors rely on electric fans and they do work well providing everything else is OK as well. I still have the original fans and original cooling system on my Interceptor and rely on that. Last time at the Ace Cafe it took me more than 1.5 hours to cover the 6 or 7 miles to get there and the fans were on just about all the time. Temperature went up slightly of course but nothing excessive. They work and work well. You can have a simple on/off system like in the Interceptor originally or you can do as Steve suggested and go for a more comprehensive system with controllers and so on. Depending on the heat generated by your engine and the cooling requirements you possibly don't need fans quite as powerful as what Steve suggests but with a controller it will only draw the power as required at the time. I think my fans draw about 18amps each at full blast which is just about 200watts each.
Once you have a system setup, I think you'll find you can relax and forget about the temperature gauge. I do.

[Richie]

Though kind of on topic, I'm going off car if that's alright. I was surprised to hear the fan running on my mk1 golf whilst cruising at 70 on the m4 today on my way home from work. The weather was of course rather warm. It didn't overheat, (or do this on the way to work this morning when the weather was of course cooler) but the gauge was past the middle and the fan whirring away... The switch operates on the same on / off basis as a an interceptor but i wouldve thought that at that speed, the fan isn't going to be achieving much and I would've expected the air flow to be sufficient to keep the temp lower though the weather was of course warm... Once I was stuck in traffic on the exit slip road, the fan brought the temp down and the fan cut out. I realise I'm on the wrong forum but i know that there a lot of knowledge on here. So, does this sound normal for an 'old school' car like the mk1 golf?

[Steve Payne]

My guess would be if the cooling system is correctly filled the radiator is partially blocked or maybe the switch that puts the fan on is putting the fan on to early.

On a motorway a cooling system even in the temperatures we had today should have enough capacity on a standard engine not to need the fan. If the radiator is partially blocked with rust or lime scale the heat being produced by the engine is greater than the radiator can dissipate so the fan will come on.

Steve

[Steve Payne]

As a general rule an electric fan pulls about 10amps per 1000cfm. In my experience and engine on idle needs about 2500cfm to keep it cool, a smaller fan will work but if it stays on (unless on a variable fan controller ) for more than 50% of the time it is to small. What you need to think about are the times when you get an extreme. Say you have just driven up a steep hill overtaking all the cars and there are some traffic lights at the top that are stuck on red and the outside temp is 30+ deg? Even a lot of modern cars would struggle with that scenario let alone cars that are marginal at best.

If you have cooling fans that can flow double the required amount of air you will never need to look at the temp gauge again. Next time you are in traffic with your modern car listen how long the cooling fan is on, my guess it will come on for 10 or 20 seconds and sound like it will suck in small children but when it switches off you wont here it again for about another minute. With modern electric fans reliability is not normally an issue and if you fit a manual override that is a belt and braces approach.

Steve

[Chris_R]

Are you not just thinking of Interceptor cooling with that requirement? I can't imagine a 1098cc Mini or Morris Minor needing that amount of cooling. Surely the cfm you need depends on the amount of heat being generated and therefore depends on the engine size. The bigger the engine, the more cooling you need, the smaller the engine, the less cooling you need.

[Steve Payne]

Are you not just thinking of Interceptor cooling with that requirement? I can't imagine a 1098cc Mini or Morris Minor needing that amount of cooling. Surely the cfm you need depends on the amount of heat being generated and therefore depends on the engine size. The bigger the engine, the more cooling you need, the smaller the engine, the less cooling you need.

Yes obviously a 1098cc engine wont need a lot of CFM but you would be surprised at the size of fans fitted to a lot of modern vehicles and I am sure they don't do it just because they can.

Some examples

1600cc Golf 2000CFM
2000cc Galaxy 3000CFM
1900cc Transporter 6500CFM
Audi A6 3000cc 6000CFM
Focus 2000cc 3800CFM
Corvette 6200cc 9500CFM
Saab 2300cc 4000CFM

I know most modern vehicles have A/C but when look at the above you can see that these must be fitted for a reason. The Audi, Transporter and Saab fans are controlled by a dual speed controller and the Golf fans are dual speed.

Steve