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Old 02-28-2008, 01:25 PM   #11
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i know bigger engined cars have plastic fans but they have a heavy steel hub that bolts to a pulley. Then ya got the all steel fan (blades and all) and i took mine iff my truck felt liek ti weighed about 15 lbs, thast 15 lbs of rotating metal that the engien didnt have to use gas/torque to rotate anymore.

Electric fans dont draw all that much current, thier lighter, and are only on off when ya want it. i would LOVE to switch my chevette over to an electric fan but theres no room an di dont think the alternator can keep up. its only a 60 amp alternator, at night when its idiling at 200(not supposed to be but it runs nice and smooth there and uses less gas than if it were at its usuall 800 rpm) i can watch the headlights dim when i apply the brakes :P
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Old 02-28-2008, 04:01 PM   #12
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IMO electric fans are better for your vehicle. I was reading one of the towing forums, one of the interminable arguments about which vehicle is mantruck enough to tow what. Started I think by a question about a minivan towing a pop-up camper.... anyway, a couple of guys were swearing their previous F-150, ford Ranger, S10 etc overheated and blew up trying to tow a pop-up over the rockies, and then there's others saying "I did it with my Windstar/subaru/odyssy no problem!" and I begin to see the connection.... the vehicles that made it, had electric fans, the improbably large trucks that didn't, had mechanical fans.... so what's going on?

Long steep grades with a big truck, the drivers will figure they've got plenty enough torque to keep it rolling, and slog it up at 1500 RPM, it moves, but with the engine under load, it gets hot.... hotter than the relatively slowly spinning fan can cope with... whereas the electric fan vehicles... the fan might have been blowing full speed all the way up, but it provided enough cooling to make it. There was someone with an ounce of common sense, telling the truck guys that pulling on a long grade especially at altitude, they NEED to change down to a lower gear to have the fan turning fast enough to do anything. They wouldn't have it of course, and had traded in for F350 superduties etc, that they are probably going to kill the exact same way. Kind of entertaining to read some of the attitudes there...

Anyway, I charge the mechanical fan with overcooling under light load conditions, resulting in worse efficiency from the motor, and undercooling in high load, lower RPM conditions, resulting in overheating and possible damage. This is apart from any losses. Vehicles designed with electric fans, I notice barely use them in normal driving when the cooling system is working correctly. I know in my driving in my vehicles, I think you can count the total minutes per month that the fan is running in hot summer driving on your fingers.
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Old 02-28-2008, 06:23 PM   #13
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Water pump speed is also a factor in a low rpm haul up a steep hill. I was thinking of adding the variable speed to my stock fan but I think the ECU maybe controlling it because it turns on with the A/C when it needs it even when the water temp is not 205 degrees that usually turns it on. I would also like the keep it from reaching 205 degrees since that give less margin should more throttle be applied making it even hotter - a 5 degree rise can occure in a few seconds with heavy throttle use.
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Old 02-28-2008, 06:43 PM   #14
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Water pump speed is also a factor in a low rpm haul up a steep hill. I was thinking of adding the variable speed to my stock fan but I think the ECU maybe controlling it because it turns on with the A/C when it needs it even when the water temp is not 205 degrees that usually turns it on. I would also like the keep it from reaching 205 degrees since that give less margin should more throttle be applied making it even hotter - a 5 degree rise can occure in a few seconds with heavy throttle use.
while I agree with the idea, I'd MUCH rather leave the water pump always active and put adjustable louvers on the grill/radiator.

I definitely agree with the overcooling bit. even with a full grill block, my S10 dropped from 175 to 120 with one moderate acceleration up to maybe 40 mph. lame turd of an engine can't keep itself warm at all full grill block and 1/2 radiator block and it finally gets and stays warm in the current weather.
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Old 02-28-2008, 09:06 PM   #15
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while I agree with the idea, I'd MUCH rather leave the water pump always active and put adjustable louvers on the grill/radiator.

I definitely agree with the overcooling bit. even with a full grill block, my S10 dropped from 175 to 120 with one moderate acceleration up to maybe 40 mph. lame turd of an engine can't keep itself warm at all full grill block and 1/2 radiator block and it finally gets and stays warm in the current weather.
hehe mine overheats(starts to) with a full block and anythign warmer than 40*F out

the e fan always turns on when the AC is on, its what cools the airconditioner condenser so it works right and blows cold air (ever wonder why your homes AC has a fan that kicks on and off?) thats part of the reason why when you turn your AC on the mpg drops from the fan runnign and the clutch grabbing and turnign the compressor
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Old 02-29-2008, 06:20 AM   #16
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Anyway, I charge the mechanical fan with overcooling under light load conditions, resulting in worse efficiency from the motor, and undercooling in high load, lower RPM conditions, resulting in overheating and possible damage.
Makes sense, because the designers usually used a fixed drive ratio for the fan (because that was easy to design/build), so it had to be a compromise with RPMs as to how much cooling you did.

But the mechanical fan still should "win" in efficiency (i.e. lower load on the engine, for a fixed amount of cooling) over the electric fan, due to the inefficiencies in both the alternator and the electric fan motor. So while the mechanical fan has two serious problems (both related to a lack of proper "regulation" of that fan), it does have one "win" on it's side. And since this is the "experiments" forum, I thought I would propose a "crazy idea" that just might (if reality matches theory) solve both of the limitations of the mechanical fan.

Specifically, why not splice a small (it only needs to handle the stresses of driving the fan) electrically shiftable gear box (i.e. the box comes pre-assembled with electric controls for when you want to do the "shifting") into the fans's drive assembly? While not specifically designed for cars, such "gear boxes" (the various "planetary gears" on the market might be a good choice) are pretty much "off the shelf" items for a variety of industrial uses (although you might have to mail-order one from an industrial gear box maker). And as such, they can be had in a huge variety of sizes, gear ratios, etc. And depending upon the room in the vehical, it might be pretty easy to splice one of these boxes into the fan's drive assembly (splicing the fan's drive shaft might be easiest, but you might not have enough clearance in your car, depending upon how the fan is mounted right now). And if you get a box that comes with a real (accessible via the built-in electric controls) "neutral", you effectively also have a "fan off" (because when your fan's box is in "neutral" the fan is no longer connected to its mechanical drive power source, so you don't get the extra cooling, and the fan's drag on the engine goes away as well)!

And if someone did go this route, remember that once you have electric controls to "shift gears" (as well as disconnect drive power from the fan), it's pretty trivial to design the rest of the fan controls to control when the fan is in "low" (stock 1-1 gearing), "high" (the "high gearing" in your gear box), or "off" (neutral gearing). In fact, you could probably use fairly stock "electric fan" controls (for example engine/radiator thermostats) to control the "gear box" of the fan. So this arrangement would (in theory) give you the control of the electric cooling fan (it's just you would now be controlling the gear box), while also giving you much of the efficiency (while actually cooling) of the mechanical fan. So in theory, this should be the best of both worlds. But I admit it is an "out of the box" way to design things...
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Old 02-29-2008, 01:40 PM   #17
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hehe mine overheats(starts to) with a full block and anythign warmer than 40*F out

the e fan always turns on when the AC is on, its what cools the airconditioner condenser so it works right and blows cold air (ever wonder why your homes AC has a fan that kicks on and off?) thats part of the reason why when you turn your AC on the mpg drops from the fan runnign and the clutch grabbing and turnign the compressor
yea, my cressida starts to heat up a lot with a 1/2 grill block over 40f

the condenser fan has far less to do with the MPG losses than say... the compressor. esp. since any decent condenser fan is operated via thermostat on the condenser outlet.

As for the efficiency of a mechanical vs electric fans. yes, a mechanical fan has less losses due to inefficiency. The reason it nets better mpg is because you can turn it off when not needed, which depending on the engine and vehicle, can be a lot. my truck would barely need to run the e-fan at all in the current weather and sould gain much more than my cressida which as mentioned above, is overheating with partial grill blockage when it's 40 and would need the e-fan on a lot more.
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Old 03-01-2008, 12:13 AM   #18
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Makes sense, because the designers usually used a fixed drive ratio for the fan (because that was easy to design/build), so it had to be a compromise with RPMs as to how much cooling you did.

But the mechanical fan still should "win" in efficiency (i.e. lower load on the engine, for a fixed amount of cooling) over the electric fan, due to the inefficiencies in both the alternator and the electric fan motor. So while the mechanical fan has two serious problems (both related to a lack of proper "regulation" of that fan), it does have one "win" on it's side. And since this is the "experiments" forum, I thought I would propose a "crazy idea" that just might (if reality matches theory) solve both of the limitations of the mechanical fan.

Specifically, why not splice a small (it only needs to handle the stresses of driving the fan) electrically shiftable gear box (i.e. the box comes pre-assembled with electric controls for when you want to do the "shifting") into the fans's drive assembly? While not specifically designed for cars, such "gear boxes" (the various "planetary gears" on the market might be a good choice) are pretty much "off the shelf" items for a variety of industrial uses (although you might have to mail-order one from an industrial gear box maker). And as such, they can be had in a huge variety of sizes, gear ratios, etc. And depending upon the room in the vehical, it might be pretty easy to splice one of these boxes into the fan's drive assembly (splicing the fan's drive shaft might be easiest, but you might not have enough clearance in your car, depending upon how the fan is mounted right now). And if you get a box that comes with a real (accessible via the built-in electric controls) "neutral", you effectively also have a "fan off" (because when your fan's box is in "neutral" the fan is no longer connected to its mechanical drive power source, so you don't get the extra cooling, and the fan's drag on the engine goes away as well)!

And if someone did go this route, remember that once you have electric controls to "shift gears" (as well as disconnect drive power from the fan), it's pretty trivial to design the rest of the fan controls to control when the fan is in "low" (stock 1-1 gearing), "high" (the "high gearing" in your gear box), or "off" (neutral gearing). In fact, you could probably use fairly stock "electric fan" controls (for example engine/radiator thermostats) to control the "gear box" of the fan. So this arrangement would (in theory) give you the control of the electric cooling fan (it's just you would now be controlling the gear box), while also giving you much of the efficiency (while actually cooling) of the mechanical fan. So in theory, this should be the best of both worlds. But I admit it is an "out of the box" way to design things...
neat idea but WAY TO EXPENSIVE!!!. Efan can be done for less than $30 and wired up in about an hour...

most cars nowadays have a oversized alternator, meanign it has alot of spare amps its generationg away that you could be using
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Old 03-01-2008, 12:05 PM   #19
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neat idea but WAY TO EXPENSIVE!!!. Efan can be done for less than $30 and wired up in about an hour...
If memory serves correctly (I did an internet search for pricing a while back), some of those small industrial "planetary gears" (with electric controls) aren't very much more expensive than that. Remember, you do not need a big gear box for this, as the only thing you would be running with this gear box is the fan. So any gear box big enough to handle the stresses on the fan (along with a little "safety margin") would do.

Of course, you are correct that this would take more time to buy/install than simply swapping in an electric fan. But the main reason for that, is electric motors are available everywhere, whereas with my idea you would have to carefully decide what gear box you want, mail order that gear box from some gear maker, and then modify the fan mountings to include the gear box into the (existing) fan drive assembly.

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most cars nowadays have a oversized alternator, meanign it has alot of spare amps its generationg away that you could be using
The point is not that you won't have enough power to run an electric fan. In most cases you will (as you mentioned) have more than enough power available.

The point is that it is likely to be MORE DRAG on the engine (and therefore LOWER FUEL ECONOMY) to run the electric fan, than to run a mechanical fan (due to the inefficiencies in converting to electric power and than back into mechanical power). Remember, electricity is NOT FREE in a car, even if/when you have extra capacity left in your alternator. Extra capacity left in your alternator means that you have the ABILITY to make that extra electricity, BUT that extra electricity will still come at the COST of additional drag on the engine (i.e. LOWER FUEL ECONOMY). And since alternators aren't anywhere near 100% efficient (in turning mechanical power into electrical power), you actually pay significantly MORE DRAG than the the equivalent electrical power you get out. And converting that electricity back into mechanical power (i.e. an electric fan) also isn't 100%, so you get additional losses doing that. Which is why using the mechanical power directly should (if you don't have a lot of lost power in the drive shafts/belts/etc) be significantly more "efficient" (engine drag, and therefore fuel economy, wise) than going with the electric fan (powered by the car's alternator)...

Which is why I was thinking that my idea (of adding electric controlled on/off and speed controls to an existing mechanical fan) might actually give the OP the "best of both worlds", in that he would retain most of the energy efficiency of a mechanical fan, but also get the cooling (and energy savings) controls that come naturally with an electric fan. All this for the cost of selecting and mounting a properly sized electrically controlled "gear box" into the existing mechanical fan arrangement.

Anyway, that's the theory. The OP is free to take it or leave it...
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Old 03-01-2008, 05:13 PM   #20
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My gut feeling would be that the electric clutches or solenoids necessary to actuate a part time mechanical fan would likely eat nearly as much as the efficiency difference.

Edit: though I guess one could rig a mechanical system with a thermostat force amplified with a vacuum servo off the vacuum reservoir.
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