I've never heard anyone talk about this, but mechanically driven fans are very consuming... Motor trend made a video testing out different types of fans on a small block, and though a thermal clutch fan seems to be the most efficient out of those that they tried, (direct drive steel fan ate just over 30 ponies) it still isn't exactly ideal...



Yeah...
It did occur to me that the test subject is a V8, which is nearly double operating speed of a diesel, and therefore the diesel would have less wind drag at high curves. The effects of any fan are going to be way less noticeable at lower RPM since wind resistance is exponentially proportional to velocity. I would still think that it's significant enough of a performance drop to consider going electric. Reliability would be questionable for me personally though, I generally tend to stay away from electronic devices in my engine compartment. One may want to consider keeping the original fan in the trunk on long road trips in case something breaks and you get stuck in a hot place with no fan... That's another thing, if you overheat you can continue to keep an electric fan on as long as you want. Not only that but you can make it go max speed without the throttle.

A (rather large) 150 watt fan equates to about ~.2 HP drag on the alternator.

Are electric fans just a thing everyone uses that I don't know about yet? Or is there a reason people don't like them? Maybe with a diesel the drag is too minimal to count. I know that my friend's Audi Q5 (diesel with same rev range) uses electric fans, and I'm sure a lot of or maybe even all new cars use them.

Here's the video:
https://www.youtube.com/watch?v=ZXdLgaFXZzs

What's everyone's opinion on this? Anyone here go electric? Share your reasoning whatever your preference

First of all, I can live without yet another Amsoil commercial. As for the substance of the video, they are mostly right.

The power consumption of a fan will depend on the aerodynamics of the entire assembly, including the radiator, shroud, engine bay, grille design. Change the fan, and the performance curve changes. So it's not as simple as saying that a plastic fan draws more power than a clutch...it depends on the aerodynamics of the fan more than weight, material or any other factor. For that reason, it's a shame they didn't test any true flex fans, as I'd be interested to understand how those respond. The various fans they did test were all designed to move a lot of CFM, not to minimize power consumption. The question of how much CFM each fan was moving wasn't addressed, it would have been a valuable data point.

They didn't quite capture the intent of a clutch fan. A clutch fan is designed to just about freewheel when it's cold. When it's hot, it engages but doesn't completely lock up. Instead, it's rev limited by the viscous clutch to prevent the sort of runaway drag that you saw with the fixed blade fans. So a cold test means little.

The more impedance in the system, the more power the fan will require, I have no idea why they were expecting anything other than what they observed: remove the shroud and HP is reduced (but so is airflow through the core).

The power consumed by a fan varies with the cube of RPM, but CFM output varies directly with RPM. Again, no surprise that a fan draws much more power at high RPM for only a little bit more airflow. A fixed blade fan on a high revving engine will swallow horsepower for no purpose. If the clutch fan had been allowed to heat up, it would have drawn much more power than it did.

By contrast, electric fans draw a constant amount of power (we'll leave PWM controlled fans aside). The dual aux fans in my 190D draw 300 watts, on high speed. Allowing for efficiency of 85% each for the fan motors and for the alternator, and the mechanical power required is a bit more than half a horsepower. They draw about 3000CFM, which is adequate to cool the engine under pretty much all circumstances. Relocated to the back of the radiator, they are all that would ever be required.

So why not just use the electrics? First, they are noisy. Second, running them full time would require an alternator upgrade, which would require a wiring upgrade. I've done a halfway measure, and I've used a Porsche fan switch to have them come on at lower temperatures, but I haven't removed the clutch fan. I found that the strain on the alternator was too much. After going through one alternator, I used a higher set point to turn them on, but still not as high as stock. My clutch fan rarely engages. However, the improvement in power isn't palpable. I'm sure it's there, but at least on my 190DT, there's enough HP to make the additional couple of ponies unnoticeable. I guess a slug is always a slug.

It's a project that could be worth doing. Especially if you are running a non-turbo 123 with the heavy aluminum fan and an 80 HP motor. Use a single big fan behind the radiator, with a PWM controller and thermistor. Ditch both the mechanical fan and the aux fans, upgrade to a big alternator. But then a big alternator requires a serp belt system, so the mods continue...

Why would you keep electric fans on all the time? That would be massive waste of energy.

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CENSORED due to not family friendly words

I misstated. I'm not running them full time. Rather, I'm switching them on at lower temperatures, in order to rely on them for primary cooling.

I can tell you my testing on gas powered V8 dodges did not result in any fuel mileage gains that I was able to notice. I've gone from metal and plastic clutched fans to OEM replacement electric and aftermarket with controllers. I've tried high temp settings and extremely low.

My conclusion in my testing was that the clutched fans operate efficient enough. I personally hated the noise clutched fans make when they are revved all the way up. Or it could be screwed testing because no matter what you can't increase fuel mileage on a gas powered dodge.

Pretty much yes.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap

I'm not a fan..
Ah ah ah. Sorry, had to

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'85 300D - federal spec, built in late 84. 85 300D Complete AC System Rebuild

Well..an electric fan can strand you in a town far away from your home and without any reasonable mechanical help available ...

My Lincoln almost did that to me a couple of months ago..

my totally mechanical 240d fan mounted on the water pump shaft with NOT even a viscous clutch to go wrong is about the most satisfying and reliable design imaginable ...a spare fan belt is easy to carry in the car..... the fan is also noisy and takes away some hp which might be saved by those other items...
but if you like a diesel due to the lack of Electrical system dependence on high voltage delivered to spark plugs at precisely the right time...... a strictly mechanical fan arrangement is simpatico in that orientation and philosophy.
One moderator told about I think his college years where his starter did not work in his manual shift Mercedes....and he was able to regularly park on a hill to get it going... and another member drove across several states after all his electrics went out.. by leaving the car running at night...

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

So what you're saying is, your 240d is even slower and less efficient than stock.

Have you heard of glow plugs?

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The Mercedes 240d comes STOCK with the mechanical fan...

I know that a Mercedes engine with good compression with sufficient rpms due to a rolling start will start and run just fine.

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

Diesel engines don't need glow plugs to run. They only assist in starting in cold weather.

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Stop paying for animal enslavement, cruelty, and slaughter. Save your health and the planet. Go vegan! I did 18 years ago. https://challenge22.com/

DON'T MESS WITH MY MERCEDES!


1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 350,000+ Miles

Electric fans will only leave you stranded if you are stuck in stop and go traffic. If you can move at least 30 mph then you are exceeding what the best fans can do. I have electric fans all of my cars, 7 of them, and have never been stranded.

OEMs have been using electric fans for decades as the primary cooling as they save fuel and reduce NVH. The only vehicles that come with mechanical fans are off road or heavy duty vehicles that are expected to do towing or hauling heavy loads at high horsepower levels.

Are mechanical fans more reliable? I have seen blades come off and rupture the radiator after years of fatigue. I would argue you are more likely to break your water pump belt due to the higher loads that are constantly on it with a mechanical fan. I doubt any real studies have been done on it.

It might be more than you need but I've been around the block with electric fans lately. I've put a OM603 into my w123 wagon and there's simply no room for a mechanical fan and a radiator. Below is the link to some of the issues I've looked through. I'm not at all concerned with the fans failing me or being less reliable than a mechanical fan.

603 in a w123 wagon

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Onus probandi incumbit ei qui dicit, non ei qui negat

I recondition w123/w126/w124/w140/r107/r129/ steering boxes!


1984 300D "Elsa" odo reset 6/2011 147k
1983 300TD "Mitzi" ~268k OM603 powered
1995 E300 "Adelheid" 262k [Sold]

Electric fans came about mostly for front drive cars that would have difficulty in bending a drive belt around towards the radiator.

An electric fan could consume less _overall_ power because they can be completely shut off unlike a clutch fan where it will still consume some power when disengaged.

An electric fan would be great for a car that has excess cooling capacity and runs at light loads. This would not be so good for a large truck where the loads are high and road speeds slow.



Prechamber diesels can be difficult to start without glow plugs and run poorly when the tips are burned off. The mechanical portion of the glow plug is a hot spot even when the electric is shut off.

I repair light towers and such for a local scrap yard, they don't run so well cold when the tips are burned off. ( RE the cylinders with burned tips miss fire for a while until the engine has enough heat in the combustion chamber. )



Noise is very related to shroud and blade design.



Gee, pneumatic tires can go flat and leave you stranded, better off to stay with solid rubber.

I appreciate everyone's input on this, good thread

I agree with this. These aren't ever very likely to break, I'll reiterate that solid tire comparison someone else made. But like I said, I would leave the original fan in the back of the car in case.

While I agree with this, it's only 3 wires and a relay holding you back, connected to the chassis and not directly do the engine itself. Incomparable to an electronic ignition system. I think I appreciate electric fans more for their versatility than anything. Plus on wintry days you can turn them off.