Mechanical fan better than Electric Fan

[PoorManQ45]

Found this on another forum.

robinhood4x4 (Mechanical) Jun 2, 2004I'm currently having a debate on whether converting from a pulley driven clutch fan to an electric fan really has any significant effect on perceived power and mileage. This is for a 3.0L V6 from a toyota 4runner. It has 150hp and 180 ft-lb torque and a plastic fan.

I'm arguing that an electric fan does not improve power or mileage significantly, or even noticably.

My thoughts for fuel efficiency go like this: The electric fan has to get its energy from the engine via the alternator, wires/battery, and finally the fan's electric motor. That can't be very efficient converting from mechanical to electrical back to mechanical energy. Certainly the same, if not worse than losses in driving a pulley all the time. Also, assuming a mechanical fan and an electric fan puts out the same CFM, the aerodynamic drag should be about the same.

For the power side of things: For drag racers I can see why getting rid of the mechanical fan and reducing the rotational mass on the engine will gain perceived power, since every 1/10 of a second counts. The less rotating mass allows the engine to rev up faster. But for the everyday driver is it really going to make much of a difference when you're trying to pass the chevy tahoe in the next lane?

So my question is, does an electric fan improve mileage and power for an engine that originally had a fan with a clutch? Also, why are most rwd vehicles equiped with a mechanical fan and not electric? Reliabiliy? (I realize fwd cars have their engines sideways and can't have a mechanical fan.)

I switched to electric (a 2speed ford taurus fan) and didn't notice any mileage improvements and may or may not have noticed power improvements (might be all in my head).

patprimmer (Automotive) Jun 2, 2004Mechanical fans are more efficient if you measure the power consumed per mass of air moved, however the electric fan equipped with a thermostat, only operates when required.

A clutch equipped mechanical fan should be better than an electric if the clutch fully disengaged, but they don't. they just reduce the drive.

Fans are greatly over sized for normal circumstances, as they must have sufficient capacity for the worst case scenario.

Therefore on overall balance electric fans, or a small clutch fan with electric boosters offers the best efficiency.

This does not mean you have more overtaking power, unless you have a switch that disables the electric fan at full throttle.

Just an aside. Drag racers worry about 0.001 of a second, and they have 4 advantages of running no fan, being, less weight, less rotating weight, more access to engine components, no belt to come off.

Regardspat [email protected], by professional engineers for professional engineersPlease see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.robinhood4x4 (Mechanical) Jun 2, 2004So for the average car enthusiast is switching to an electric fan really going to make much of a difference in fuel efficiency?

Also, the guy I was debating with pointed me to a mustang page where they said, "Swapping out a clutch fan will still net 10 -15 horsepower as the rpms increase." I just don't believe it would make that much of a difference. Here's the page: http://www.fordmuscle.com/arch...shtml

TChronos (Automotive) Jun 6, 2004Power consumption for a given fan will increase with respect to the cube of the change in RPM

HP2=HP1*(RPM2/RPM1)**3

This means that for a simple fan, power consumption can be enormous at high RPM. A viscous clutch will reduce HP consumption by limiting RPM.

All things equal, an electric fan would be limited to some fixed speed, typically under 2500 RPM. This would reduce power consumption above that engine speed. A huge electric fan would consume about 370 watts, less than half a HP.

If you powered the same fan blade directly by the engine, it would consume about 13.5 horsepower at 7500 RPM. Warpspeed (Automotive) Jun 6, 2004I think the difference in power or economy would be very difficult to even measure on a practical road vehicle.

There is one other issue though, reliability. OEM electric fans seem to be very reliable, but the cheapy hardware store do it yourself kits often turn out to be expensive improperly installed crap.

If you want to do this, try and use a decent fan motor and controller. The same goes for electric water-pumps. Great idea in theory, but if it fails, it could end up in lots of tears.ejit (Automotive) Jun 10, 2004All responses missing the major point.Above about 35 mph (+/-depending on the vehicle, grill area, etc.) you don't need a fan at all.Highway speed: belt driven fan is power completely wasted, electric fan is consuming NO POWER.

patprimmer (Automotive) Jun 11, 2004Quote:however the electric fan equipped with a thermostat, only operates when required.[quote]A clutch equipped mechanical fan should be better than an electric if the clutch fully disengaged, but they don't. they just reduce the drive.[quote]Quote:Fans are greatly over sized for normal circumstances, as they must have sufficient capacity for the worst case scenario.

I think the above quotes did cover your point, except for the 35 mph, which is a very rubbery figure anyway. I have seen cars that overheat at 50 mph with no fan at all, and some that run quite nicely at 20 mph.

Regardspat [email protected], by professional engineers for professional engineersPlease see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.Metalguy (Materials) Jun 12, 2004I like electric fans. Had a Chevy pickup with 454 and the stock fan clutch. This truck came with a BIG 7 blade fan, and when driving along the truck would suddenly slow down when the clutch started driving the fan "at speed". The single v-belt would also squeal a bunch, and the fan roar could be heard easily.

I changed it to a direct-drive stainless steel fan with flexible blades.turbododge (Automotive) Aug 23, 2004A couple of points to consider. If you go electric, you may need to upgrade the battery and/or alternator to handle the extra load, or you could be dead in traffic. I have found that having a clutch fan SIGNIFICANTLY reduced (by almost 100*F)and evened out underhood temps. This is of particular interest if you are carbureted, as the wide temp swings can really make tuning the mixture difficult. On a FI engine, the programming should do a temp correction to get the right mixture, but the extra temp can cost you power, especially at lower speeds, or accellerating after idling for a while. I went to a clutch fan on the twin turbo 340 Chrysler a few years ago (from electrics), haven't noticed any drop in power, but run much cooler with less problems.

evelrod (Automotive) Aug 23, 2004On my vintage racing mini, because of the rad placement and 'weired' aero, the mech fan is a must. I have an elec. fan (thermostatically @ 200f and mech switched) on the outside of the rad but, it alone (even at 100+ mph on a hot day) is not sufficient to keep enough airflow through the rad to avoid 220f water temps. 1275 Mini's are notorious for overheating when power is boosted to 130hp or so in competition. I use the smallest mech fan I can and it has blades that use a NACA undercambered airfoil for effeciency.A couple weedends ago at California Speedway in Fontana it was 96/97f and speeeds were in the low 120 mph range. Water temp was 180f and oil was 170f (19 row Mocal fully ducted). The elect fan only came on cruising the paddock (I have an indicator light). It's all about airflow. If an elect fan will do the job, it's the least obtrusive method. As Pat says, no fan blade to get your fingers into and no belts to through.As to hp requirements of my setup---~1/2 hp at ~3500 rpm and ~5 hp at 7200 rpm measured on the dyno. By shunting the alternator I gained back an estimated (did not have a shunt when we did the dyno run)~4 to 5 hp so I now have a switch for that also. I'd rather stay cool than worry about any small hp loss. One of my competitors (nice little red mini) lost a ~$1500 cyl. head because of 300+f temps that weekend!

Nothing is black and white, it's a grey area. You need to go with what works for you and not what Joe Blow is using.I put a lot of research into what I build. It's a lot cheaper than "suck and see". Besides, all the scratch pads impresses the crew. They actually think I know what I am doing. ;o)

Rodharrisj (Automotive) Aug 27, 2004Came across an interesting electric fan conundrum a few years ago on a brand new Citroen.......

Engine consistently overheated on the open road in summer, especially when towing. Stop the car and the engine temp went right down again. Fine in heavy traffic, even for an hour at a time. OK when climbing steep hills. Strange....

Solution? Citroen had wired the fan back to front, so it pushed air out forwards through the grille!

Seems obvious, but it took a while to figure. Just a tale for those of you fitting aftermarket electric fans.

JohnTomOstrowski (Automotive) Aug 29, 2004Optimal placement for an electric fan(s) for a traditional forward-mounted radiator is behind the radiator, on the side closest to the engine, so the fan is sucking air through rather than in front pushing air through the radiator. Quite a few people who buy aftermarket electric fans incorrectly assume they go out in front to push air and then are unnecessarilly dissatisfied with the results.

OpenSourceCar (Automotive) Sep 3, 2004If you use an electric fan you can always wire your alternator (field windings, not output), or the fan relay through a NC limit switch on your throttle so that when you floor it, the alternator or the fan cut off. I did this with my alternator and AC compressor and used a small solid state delay module in line so that it stayed off for at least 15 seconds. It made a big difference to overtaking and the battery can cope fine with the extra draw now and then (even with the lights on.) cheers, derek

[IvoryJ30t]

the only time i remove a mechanical fan in favor of electrics is when the viscous clutch dies.

in that case, spending the money on an electric fan, thermo switch, and the massive hp draw from a malfunctioning clutch make the conversion worthwhile.