Jump to content
If you value this forum's future please support us
GBMUD

Electric fan or mechanical? Facts here!

Recommended Posts

GBMUD    21

I know people are always asking, and I have aired my opinions often enough.  Watch this video for some actual measured figures.  Keep in mind though, their graphs do not start until 3000rpm and I pretty much never exceed 3000rpm in my diesel Defender!

Chris

 

 

 

Share this post


Link to post
Share on other sites
SPendrey    18

So Land Rover may have got it right?!  It wasn't clear if the viscous fan itself was heated up to "lock" it, then see how much it consumes.

Share this post


Link to post
Share on other sites
Bowie69    382

Yep, watched that this morning, and yes, even the viscous unit caused a fair old bit of drag.

There is a reason why electric fans are fitted to almost every modern vehicle.... once you are up to speed they don't need to run.

They stated in the video it was cold in there and the viscous fan was not locked up, still it consumed power.

Have to say, the yanks do make me chuckle when they talk about electrics, they seem to think they are some fragile thing that will go bang every time you touch them... 'Electric fans use so much juice they will put a huge load on the electrical system'... err, 30A? What about your heated rear window, windscreen....?

Like anything, engineer it properly and electrics can be as reliable as you want them to be.

Share this post


Link to post
Share on other sites
GBMUD    21

I would argue that the viscous fan unit should have been warm - normal running temperature - for the test as they do become less viscous when warm and only 'lock-up' when hot and extra cooling is needed.

Chris

Share this post


Link to post
Share on other sites
Snagger    197

These guys really are clueless.  They didn't test how much air any of the fans shifted, so there was no comparison of their efficiency, just their power consumption, and the test is irrelevant because nobody does 4000rpm stationary for extended periods - as soon as the vehicle starts moving, the airflow through the rad reduces the angle of attack of the fan blades and reduces its drag.  They also clearly don't understand the airflow through or around a fan; of course an unshrouded fan consumes less power than a shrouded one on a static run - the fan creates a torus of circulating air that doesn't have to pass through the restrictive rad if the shroud is missing, which is the whole reason for fitting the shroud!  All that video did was advertise an oil product!

  • Like 1

Share this post


Link to post
Share on other sites
Bowie69    382

True I though expect some warmth would have been conducted from the water pump to alleviate that, at least somewhat :)

Share this post


Link to post
Share on other sites
Bowie69    382

It may not be 100% scientific, @Snagger, but it did give SOME info in there :)

Share this post


Link to post
Share on other sites
Snagger    197
5 minutes ago, Bowie69 said:

Yep, watched that this morning, and yes, even the viscous unit caused a fair old bit of drag.

There is a reason why electric fans are fitted to almost every modern vehicle.... once you are up to speed they don't need to run.

They stated in the video it was cold in there and the viscous fan was not locked up, still it consumed power.

Have to say, the yanks do male me chuckle when they talk about electrics, they seem to think they are some fragile thing that will go bang every time you touch them... 'Electric fans use so much juice they will put a huge load on the electrical system'... err, 30A? What about your heated rear window, windscreen....?

Like anything, engineer it properly and electrics can be as reliable as you want them to be.

Most engines are mounted transverse.  I think that is the reason.  The majority of longitudinal engines still seem to be engine driven.

Share this post


Link to post
Share on other sites
Snagger    197
1 minute ago, Bowie69 said:

It may not be 100% scientific, @Snagger, but it did give SOME info in there :)

I disagree.  If they had done the test in a wind tunnel to simulate the airflow from the car movement, it'd have a small amount of credibility, but not conducted static.  It is not remotely reflective of real driving conditions.

Share this post


Link to post
Share on other sites
Bowie69    382

That may be, but I think given the huge variance in engine bays, it is likely something that would have to be test on a per-vehicle basis.

Oh, and no way would I trust a flexi-plastic fan not to go through my radiator!

Share this post


Link to post
Share on other sites
Snagger    197

Just like you, I wouldn't trust either of those after market fans!  The aluminium one with the flat and cranked sections is aerodynamically rubbish and would achieve very little airflow for the drag, while the plastic fan is far too curved and would have terrible drag and next to nil airflow at low rpm, behaving like flat paddles and just stirring the torus of air it sweeps through without moving it aft.  Presumably, they were made by the same sort of manufacturers as Hiclones, vortex exhausts, fuel magnets and so on!

You're right that different engine bays would have drastically different effects, and so would different body shapes and exterior fittings like lights and winches (which block ram air, reducing rad effectiveness but also reducing fixed fan drag).  The variables are huge.

Share this post


Link to post
Share on other sites
FridgeFreezer    369

Every cooling fan thread ever...

HarryHill_fight.jpg

 

  • Like 2

Share this post


Link to post
Share on other sites
Soren Frimodt    109

I personally find Engine Masters very entertaining. And of course even more Roadkill from which it has spawned. I like how they go against all the naysayers, and all the misconceptions and prejudice that is everywhere, both on the WWW and IRL. Just take the one where they completely destroy some headers and it did nothing bad to the performance of the engine, that will have put a lot of smart-arses in there place ;) I like how finally someone does those tests that we have all been wondering about ever since we fixed our first moped :D 

But súre it isn't any exact science, but you shouldn't expect that from the show, another thing they did wrong was claiming that as the Alternator spins anyways it won't draw any extra HP, which of course it does with the higher load.

  • Like 2

Share this post


Link to post
Share on other sites
Davo    47

Damn, I just stayed up too late watching that! I've been experimenting with this for several years now, and I'm onto electric fans for the third time, and won't be going back to engine-driven. I've tried a couple of viscous clutch set-ups as well as some different systems for running the electrics, so hopefully this time I've got it. In very short form, I've learned:

- the viscous fans really did use a lot of horsepower, something you can easily feel with a 3.5 V8. They are also hopeless at hot idle, especially in really hot weather and especially after a long run at 100kmh. The Range Rover clamshell bonnet traps a lot of heat and even the venting I've got doesn't help much. 

- electric fans are really sensitive to airflow in the engine bay. If there is no decent exit for the hot air, they will run for much longer than you'd want. You really need to make sure the engine bay is as much of a low pressure area as possible - tricky on any Defender or old Rangie. You also must have just the right on and off temperatures, and the simplest wiring possible since there's a lot to go wrong. It's also really hard mounting the things to survive long stretches on corrugations - something I haven't tested yet! 

Share this post


Link to post
Share on other sites
mad_pete    59

It gives a worst case for the cooling fan shifting stationary air.  Electric fan is what ?   20a x 12v = 240 W. I've hand cranked a generator in the science museum so I could believe that's about a hp.

 

ok I checked 1hp is 750w ? going to have some loses from things but what are these viscous fans doing with all that power ?

 

 

Share this post


Link to post
Share on other sites
Soren Frimodt    109
6 minutes ago, mad_pete said:

It gives a worst case for the cooling fan shifting stationary air.  Electric fan is what ?   20a x 12v = 240 W. I've hand cranked a generator in the science museum so I could believe that's about a hp.

Though you must remember that the alternator is geared pretty high from the crank pulley. So you would need to now that gearing to calculate the precise HP draw. It is actually very simple, if an electric fan is to shift exactly the same amount of air as a mechanical one, it will take more power from the motor, than the mechanical one, because of the loss in converting energies. However the mechanical of course always takes the same amount of power, whether its needed or not, whereas the electric only consumes power when its needed. So surely that must be where the saving in HP, and fuel economy is. In theory if your engine is run in hot enough conditions to always require max cooling, the electric fan would be too costly on energy compared to the mechanical?

  • Like 1

Share this post


Link to post
Share on other sites
mad_pete    59

Once locked the mech fan spins as fast as the enigine. The electric fan will spin as fast as it is set to. There is no reason to assume they would shift the same air.  

  • Like 1

Share this post


Link to post
Share on other sites
Soren Frimodt    109
32 minutes ago, mad_pete said:

Once locked the mech fan spins as fast as the enigine. The electric fan will spin as fast as it is set to. There is no reason to assume they would shift the same air.  

You're quite right, I don't think they do in most cases, however you would imagine it needs to, to provide the same amount of cooling? There's also quite a difference in speed, many electric fans run very fast, I suppose that's why they can get away with smaller fan blades than a mechanical one.

I have never been a fan (excuse the pun) of electric ones as I have yet to have a car fitted with it that wouldn't at least at some point overheat. Same problem with viscous units, they fail when its most inconvenient. However on the 80" I was forced to go electric as the amount of belts for my accessories had grown to an extend where there was no safe room for the stock mechanical one. And even though I use all Kenlowe stuff, it has overheated for me twice since, and never once with the mechanical one. Needless to say, I carry the stock fan in the tool box ;) 

Share this post


Link to post
Share on other sites
Daan    105

It is not very scientific, as more drawn power means more cooling, i'd say. Usefull when you need it. Also, most of us have an intercooler, and that changes thing quite a lot, especially at low speeds, like offroading. If you run an electric fan, the intercooler becomes a wasted part at lower speeds. So certainly, in this situation, viscous must be far better. Going fast at high RPm, it is a different situation, F1 cars dont have fans for example, as they go fast enough to cool well without them. But they can't stand stationary in the pitlane with the engine running, as they will cook very soon.

 

Daan

Share this post


Link to post
Share on other sites
mad_pete    59

The mech fan weighs more so just spinning it will take more power and I suspect there is only so far blowing more air will go to giving you more cooling.  As long as the air is enough to put the engine to warm extra cooling is wasted energy.  The mech fan cost more power than I expected although 6,500 is a lot more pushing than my fan will do. Also if the mech fail viscous unit locks shows you you probably have a few extra horses being taken so a working viscous unit is probably worth about 4 hp.

Share this post


Link to post
Share on other sites
FridgeFreezer    369

Just to throw some variables in: I have smaller twin electrics, set to come on half speed then full speed as temp rises. Pretty much never come on full speed, and draw is less than 20A at half speed.

It's zero when they're off which is most of the time, so less than any mech fan no matter how good.

Share this post


Link to post
Share on other sites
Bowie69    382
16 minutes ago, FridgeFreezer said:

 

It's zero when they're off which is most of the time, so less than any mech fan no matter how good.

I think this is the crux of it, I dislike wasting anything, especially power, and as above, even the viscous unit when unlocked WILL use power, the electric none.

Crawling at 5mph with electric fans going all the time is likely to use more power, I would say.... just due to the losses involved in converting mechanical to electrical energy and back again (alternators are only around 50% efficient at best).

That said, an engine driven fan will be designed to run the engine in 50C external temperatures, in our climate in the UK we don't really need that sort of headroom, hence electrical fans do make a lot of sense.

So... if engine driven fans consume more power for every day use, then surely there's additional fuel consumption? Let the fight begin :P

Share this post


Link to post
Share on other sites
missingsid    38

Good answers here and I realise that the topicis about losses but they are negligable really, a good reason for using electric is that it can be in front of the rad to free up space and stop/ reduce water spray on to the engine during water crossings or even turned off completely with an extra switch.

With a Series 1 rad and V8 with Kenlowe mine has never overheated in 30 years!

Share this post


Link to post
Share on other sites

They do some interesting tests like the hammered headers test that Soren mentioned, the above is also useful knowledge.

On the whole electric/mechanical fan arguement, I've deliberately made sure I've still got the option of a viscous fan when I dropped the merc lump in. On a V8 I'd happily run electrics again like I had with the 200tdi. But with an intercooled diesel, just having that airflow across the intercooler is a massive advantage and will more than make up for the power losses from the fan. Compound turbos and higher boost pressures on mine will also mean the advantage of cooling the intake air is even greater.

Share this post


Link to post
Share on other sites
Bowie69    382

So basically it comes down to application, and making it specific/suitable to your vehicle and expected use :) 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


×