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Old 02-22-2008, 08:42 PM   #1
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Electric Cooling Fans

I've read a lot of claims by members on explorerforum.com who say they've gained 2-3 mpg by removing the stock belt driven fan and replacing it with an electric one. The gain is made even more when they installed a thermostat which slowly ramps up the speed of the fan. When the engine is slightly hot it will run the fan at maybe 10% speed. Then as the engine gets a few degrees hotter the fan will increase to maybe 20% speed etc. Also, the power sent to the fan is controlled by PWM instead of heat sinks. As most of you know, PWM controls speed by pulsing the power rather than wasting it by converting it to heat.

Basically when your on the highway you don't really need a fan, and the electric one shuts off, but the belt driven one is always on even though the clutch is helping. I'm planning this mod to my explorer in the near future. Just thought I'd share the info/pass it along.
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Old 02-23-2008, 09:37 AM   #2
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^^ seems like a lot of work for the electric fan. I'd say use something similar but rather than running it at various %s as it heats up, wait till it's at or over temp, then turn it on using the PWM ramp up to prevent the acceleration current surge of the motor.

or, spend 1/10th as much on the motor/control and get a simple $20 on/off thermostat and a $50 fan and set it as above. on at say 210, off at coolant t-stat temp or a little lower
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Old 02-23-2008, 10:47 AM   #3
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yup i did this to my s-10 an dgained about 2-3 mpg (underpowered 4 banger in a heavy truck) i got the fan out of a junkyard off a cavileer(same engine) and the $20 on off Tstat from advance. works great!
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Old 02-26-2008, 09:35 AM   #4
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I was looking into some of the new style high efficiency fans. They have some now that use about 1/2 the current as the traditional style. They're much more efficient, and quiet but expensive. I've read some pretty cool installs that hardly use any power at all, and are extremely quiet. With the thermostat that runs at low speed that's sometimes enough to keep the engine from overheating, whereas if I wait until it's already at max temp I might not be able to cool it down. If I had a small engine I'd be able to get away with it, but with bigger engines I have to stay ahead of the game.
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Old 02-27-2008, 11:30 AM   #5
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thats why you have to select a fan that pulsl enough CFM to cool the car down. mine is off a late1980's 2.2L cavileer installed on my 2.2L s-10. meanign if it can cool the exact same motor in a car it can cool the exact same motor in a truck. which it does very nicely. the fan kicks on and i can watch the temp guage fall immediately.

who cares if its quiet or not! i can BARELY hear it when it kicks in at idle. I have to get out and walk to the front of the truck to tell if its running, ya notice the tiny surge from the alternator the most then it levels out. i think mine draws about 15-20 amps at startup.
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Old 02-27-2008, 11:52 AM   #6
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haha worrying about a quiet e-fan.... as if it could be worse than a mechanical fan LOL
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Old 02-27-2008, 05:56 PM   #7
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In theory, an electric fan is actually less efficient than a belt driven one when the fan is running. Because with a belt driven fan you only have the drag intrinsic in running the fan itself + the mechanical losses of the belt and pulleys (putting extra drag on the engine). But with an electric fan, you have the losses associated with the fan (same as with the mechanical fan, above) + the large inefficiencies (losses) associated with using your alternator to turn mechanical power into electric power + losses/inefficiencies in the fan's motor when it converts electrical power back into mechanical power + any electrical losses/inefficiencies in the fan's control circuitry. This means that the losses/inefficiencies in an electrical radiator fan can easily be much higher than the losses/inefficiencies in a mechanical radiator fan ("directly" driven off the motor).

BUT, the other factor in the equation is that you frequently don't need to always run the radiator fan. And with an electric fan, it is much easier to control the fan so it's run only when "needed". As a result, most mechanical fan arrangements run much more often than most "electric fan" arrangements (simply because it's easier to make fancy electric controls than fancy mechanical ones). And whenever the fan (either mechanical or electric) is running, it will lower your FE. So the primary reason why electric fans are often better FE wise, is simply because the electric fan is run less than the mechanical radiator fan (because it's easier to design the electric fan controls to shut the fan off when not needed)!

NOTE:
This does mean that if you want to use an electric fan for FE gains, you also want to do all you can to only run the fan when it really is "needed" (to keep your car from overheating).

For example, a well maintained (and "clean" on the inside) engine can safely be run a few degrees hotter than "stock" (car maker recommended) settings (especially if/when using good synthetic oil, and extra good filtration). So if your car is extra well maintained, you should be able to safely use a thermostat setting that lets the engine get a little hotter (than "stock") before the (electric) radiator fan kicks on. You can either do this by carefully selecting which fan thermostat you pick, or by (doing what I do and) picking a thermostat with an adjustable control (so you can easily adjust what temp the fan uses, without having to pull and replace the thermostat each time). Not only will this save some fuel due to the electric savings (of the fan running less), with some cars they also get better FE for being extra well "warmed up" (a double FE boost, as you get both the FE benefit from using the fan less, and the FE benefit from running a warmer engine). However, you obviously want to do this carefully (making sure your engine is well maintained for these extra stresses), as getting things "too hot" can damage the engine (in extreme cases actually melting the engine parts into a useless hunk of metal). So going "extra hot" isn't to be done without some care, but it can save FE, and shouldn't harm your engine if carefully done (so as to make sure you don't break your engine by getting it "too hot").
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Old 02-27-2008, 07:02 PM   #8
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Quote:
Originally Posted by kamesama980 View Post
haha worrying about a quiet e-fan.... as if it could be worse than a mechanical fan LOL
haha i know, mechanical fan was liek running a huge 20" box fan on high while the truck was idiling
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Old 02-27-2008, 07:53 PM   #9
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Since the whole reason of doing a conversion to electric fan is because it works on demand, I don't think it will save any money for people who drive in situations that demand it all the time. With that said, I think anyone who doesn't live in a big city, or anyone who drives more than 50% highway, will see an increase in fuel economy. Not only that, people who live in hot weather will also have the added ability to manually turn on the fan to increase the efficiency of their air conditioner while sitting in traffic at stop lights. The fan has one purpose which is to cool the fluid in the radiator. Having an old belt driven fan that runs 100% of the time seems ridiculous, especially in cold weather situations that a surprising amount of vehicles could get away with no fan at all for long periods of time.

Personally I think the belt fans are very reliable, but when we're talking about being efficient, using a belt driven fan is just like throwing money away. It might only be pennies, but either way its throwing money away.
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Old 02-27-2008, 09:04 PM   #10
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Originally Posted by gto78 View Post
Since the whole reason of doing a conversion to electric fan is because it works on demand, I don't think it will save any money for people who drive in situations that demand it all the time. With that said, I think anyone who doesn't live in a big city, or anyone who drives more than 50% highway, will see an increase in fuel economy.
True. And I agree that you frequently don't need any fan at all, especially at highway speeds and/or in the winter. So there is a lot of potential savings there.

However, with that said, I should point out that it is quite possible to design a mechanical drive fan that allows you to "turn it off". For example, you could use some sort of clutch mechanism, to allow you to (mechanically) disengage the fan from being driven by the engine. And you could even use an electric servo-motor to engage this sort of mechanical clutch "automatically" (giving you the same sort of auto-controls that are traditional with electric fans).

So while it is easier to make fancy controllers for electric fans, it's actually possible to add just as much fan on/off control to mechanical linkage designs. It might not be common practice in the industry (common practice for old mechanical linked fans is to use a very simply "brain dead" linkage), but it is clearly possible to do. And while a fancy mechanical linkage for a fan might be more of a PITA to design/build (than a similar controller for an electronic fan), a well designed mechanically linked system might actually be even more FE than a traditional electronic fan arrangement. I say that because a well designed (with a full "off" mode) mechanical linkage has the same advantages as the electric fan when not in use (i.e. neither option would put much of any drag on the engine when not in use), but the mechanical linkage option probably has considerably less power transfer losses than the electric fan option (which has losses in both the alternator and the electric motor).

So again we are down to the electric fan winning mostly because of the greater on/off control. However, if you properly design the mechanical linkage, it is possible to build a control that allows you to disengage that linkage whenever you want. And if/when you have such a "off switch" (for your mechanical linked fan), the primary advantage of the electric fan goes away (as the mechanical fan then also has the on/off as you need it option)...

That said, I'm (personally) NOT going to go to the trouble/expense to add a mechanical fan to my car, that came stock with 2 electric fans. As I see it, "The Juice Ain't Worth the Squeeze" (i.e. the benefits aren't worth the retrofit costs/hassles to me, since I've already got the electric fans). OTOH retrofitting the car to enhance the fan control options (for the existing electric fans) was considerably less work/expense, so I have taken some steps in that area (and it appears to be helping my FE some). Because while differences in fan design can make some differences in efficiency, the biggest difference is to be had in simply leaving the fan off as much as possible (subject to not getting your engine too hot, and thereby causing damage to your car)!
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