BTW Godfather,

Reading Jack's and Sburn's discussion, maybe you already have the best cooling available to you and your truck!

Lars:2thumbs:

well we shall see if i get any improvements, im not really worried about the a/c because i live in seattle and there are only about 60 days or so that i need it.


i was doing both the ud pulleys and efans for mpg gains (if any) because my mileage is really in the gutter.


i honestly hope that it helps because i drive at least 35 miles a day and im putting more miles onto the truck than i want to. now i would be ok with this if i start to get an increase in gas mileage. im only average maybe 13 mpg per tank, getting to 15 would be great.

if it doesnt really help then ill be a little mad because of all the money ive spent on mods i could have bought a cheap little commuter car but oh well at least my truck could probably beat a rice rocket if i pulled up to one. that makes the mods worth it :)

OK, to noodle the e-fan business around a little bit more, here are my thoughts and calculations. Feel free to refute, correct, debate:

Looks like the standard twin e-fan set-up (Spal, Derale, F-A-L) makes 4000-5000 CFM and take around 50 Amps (2 fans @ 25A). 50 Amps @ 12 Volts is 600 Watts. 600 Watts converts to 0.8 Horsepower. As Jack said above, there will be some conversion losses. A quick search suggests that belt-driven alternators are not much more than 50% efficient in converting mechanical to electrical power, so the engine has to turn the alternator with 1.6 HP to get that 0.8 HP (600W) out the other side.

I can find very little on how much HP is required to turn a conventional (non e-fan), other than from the folks who are selling e-fans. The often quoted 10-15 HP drag may come from a clutch-engaged fan at 5000 RPM for all I know. And the HP "savings" in that case would be 15 HP less the 1.6 HP for e-fans, in the case of the e-fans fans running full speed.


So, back to the real world:

In summer stop-and-go traffic, the e-fan may prove helpful with the added airflow for the A/C. 1.8 HP gets used to power those e-fans, but I'm not sure I care too much about losing 1.8 HP in stop-and-go traffic anyway. Having the A/C work real well is a fair trade on a hot summer day for me. The conventional fan in this situation is engaged and eating some ammount of HP, but it's likely moving less air than the e-fan, so it's likely using less HP than the e-fan.

Now, traffic clears out and I'm now zooming along at 60 MPH. e-fan are (or should be) completely off and taking zero HP. Conventional fan should have the clutch open and be freewheeling.

So at idle, the conventional fan may win the HP battle, provided you don't care about maximum A/C. And a 60 MPH, the e-fan wins since they should be off. At 60 MPH the conventional fan is disengaged, but it's still taking some HP just becasue of the mass and clutch drag.

Thoughts? Comments?

Full on, Sburn! VERY well presented post! It's what I like about this forum, people actually have brains over here and they use them!

I'm glad you did the research on the power loss, since I was too lazy/incompetent to do so. And it gives me a platform to comment.

IF, the 1.6 HP penalty is correct, and it sounds pretty good to me given the power demand figure you quote for the e-fans, then stopped at idle, it's kind of a "wash" isn't it? The e-fans are using a constant 1.6 HP, and the new PCM controlled fan's needs vary between quite low (at engine idle, since it is not turning very fast) to higher at cruising speeds - where it should be freewheeling anyway.

Now, the only thing that power demand does at idle is use a bit more fuel (in both cases) and, for the amount of time we're usually stopped, I doubt we'll feel much difference in the AC. So, the PCM controlled fan may win out in economy at idle and not make us too uncomfortable.

But, I don't know when the e-fan controller cuts it off as speed increases. I think it is purely temperature controlled, so it's possible the PCM controlled fan might cut off sooner, as a speed increase is seen?

And, since both should usually be off at highway speeds, we're left with your final statement. Is there any clutch drag with the new fan? The ram airflow through the radiator is going to encounter both kinds of fans and will try to spin them and all of this causes aerodynamic drag. But, the drag would be there anyway, since the engine and engine bay is not exactly a "slippery" aerodynamic shape. So, we spin the e-fans by airflow and get nothing in return since they are "decoupled". We spin the "water pump" fan and, if there is any clutch drag at all, we decrease its drag on engine power. But, if there's no clutch drag (does there have to be?) there's actually no power loss to the engine.

I know there was always some power loss through the fluid clutch since it is always ON. But, could the new clutch be purely (or effectively) mechanical? I doubt the new design would have been adopted if there were no real benefits. The fluid coupled fan was "simple", and it worked, but there was always drag. Maybe the drag was eliminated in the new, more complicated design?

- Jack

Thanks guys for putting numbers to this statement.
Sburn now what if any are the advantages of a viscus clutch over the traditional clutch?
I wish I knew more about that electic clutch wether or not if it's a hard lockup, partial lockup, or maybe gradual lockup?

Lars

Sburn posted the numbers, not me! And, your question that I "bolded" does sort of differentiate between something that works and something that is just "hype", doesn't it?

I know if I'd replaced something as simple as a viscous clutch, I'd go with hard lockup.

- Jack

There's two flavors of e-fan controllers that I know of. Simple Off/On at a preset temprature (~thermostat temp) and PWM e-fan controllers that vary the e-fan speed based on the temp. sensed at either the radiator or by piggybacking on the factory ECT/CHT. So, the e-fan with a smart controller wouldn't always have to be running at 100% when it's on.

I'm not yet sure how the clutch works on the new PCM fans. Could be a PWM to some kind of solenoid that squishes some hydraulic bits, or a variable DC voltage to a magnetic particle clutch. I'll have to RTFM this weekend. Or, drag out the old oscilloscope.

Ford's PID show the fan RPM sensor and PCM output to the clutch as a percentage, but I don't yet know if the percentage mean duty cycle or a voltage:

http://www.smbtech.com/fan_pids.jpg

Or, if you had access to a 2008+ truck, you could try spinning the fan by hand with the engine stopped. If you feel drag, it's going to be there anytime the engine is turning.

- Jack

So, you're suggesting I might hook a fish scale up to the fan with the engine stopped and measure the drag as torque, right? That could be good to know. Not sure about 2008+, but my 2007 does have some drag when stopped, so whatever scheme the clutch is, it's not perfect.

:hehe: I thought you said the change was in the 2008 MY. My 2005 certainly has viscous drag when I attempt to spin it by hand with the engine stopped. I haven't actually tried this, but as I understand it, the drag should be greater if the engine is hot. (I'll have to give it a try). In my engine, the fan ALWAYS turns, but, it is supposed to turn faster (closer to engine speed) with the engine hot. (I know you know this, I'm just adding it for anybody who may not understand how a viscous clutch works).

I doubt you could measure it with a fish scale though on a stopped engine. You'd need to catch the fan to a scale mounted on a rafter or something and measure the force on the stalled fan with the engine running. Then, you could calculate the torque/hp loss from this force and the distance you had the "hook" from the hub. It's not something I'd like to try, since it sounds a bit dangerous.

But, if there is NO resistance in the 2008+ line, then that is a whole different clutch! And, you should be able to compare the relative resistances in different MY trucks by feel.

- Jack