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post #1 of (permalink) Old 05-15-2007, 10:01 AM Thread Starter
 
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Clutch fan and fuel economy

Is there any appreciable improvement in fuel economy running a clutch fan? Any other benefits? Mine just has a 4 blade solid fan from a 1980 eagle 258.
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post #2 of (permalink) Old 05-15-2007, 11:52 AM
 
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Clutch fans were installed for just that reason...
Fuel economy and emissions mandates.
Less parasitic drag on the engine meant better emissions and fuel economy.

The fan free wheels after start up until the radiator heats up, and it free wheels at highway speeds when there is surplus air being forced through the radiator.
The only time your fan is 'Fully' lock up is hot idling.

Higher engine RPM's also had a part to play in it.
Obviously, higher RPM took more horse power to turn the fan, but the mass of the older fans was so great they often came apart, and they were really made a lot of noise.
Clutch fans could be built lighter weight, since the clutch let them slip when you accelerated hard, and they didn't make the noise because the clutch limited top RPM for the fans.

Clutch fans got their start in the early 60's in California vehicles (early emissions laws) and in luxury vehicles (nose concerns).
Clutch fans didn't make a complete appearance in everything until the early 70's when the 'Gas Shortage' happened, and the feds started laying down EPA and milage laws.

Clutch fans are a great idea in an off road vehicle.
They will allow the fan to disengage the water pump pulley when you hit deep water so you don't burn belts or the fan blades don't pull them selves into the radiator.
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post #3 of (permalink) Old 05-15-2007, 12:07 PM
 
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If you really wanted to keep the fans from draining horsepower, I'd suggest an electric one. The only problem with these is hitting deep water off-road and the reaction of the fan's wiring system to it, but if all you'll be doing is dry trails and rocks, I really don't see any issues as long as you bring an extra relay, just in case one burns up. I run one on the Ram for track use and I have never had a problem with it.
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post #4 of (permalink) Old 05-15-2007, 08:01 PM
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Electric fans are also a power grabber... they take about 10 - 15 HP when they're running... They usually also take a larger amperage alternator. There is no free lunch.
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post #5 of (permalink) Old 05-15-2007, 08:19 PM Thread Starter
 
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Leve, is there something I can find a clutch fan that will fit at the junkyard? aside from another 258? I don't think they used them on Dodge Caravans?
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post #6 of (permalink) Old 05-15-2007, 09:06 PM
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That's a good question.

These parts are outsourced, and likely used on several different engines. However, I don't know which would fit. I'd walk the yard with a bolt pattern template for the pulley and fan bolts and see what would fit.

Caravan? Why another one crawled into my yard... a 1999, with a bashed bumper and hatch. I couldn't pass up free. I replaced the hatch, bumper and wrap around for about $80, and now I'm working on pulling out the sheet metal... that's fun, but it's a something I know nothing about.... here's the before and the after...

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post #7 of (permalink) Old 05-15-2007, 11:04 PM
 
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Quote:
Originally Posted by TiminMb View Post
Leve, is there something I can find a clutch fan that will fit at the junkyard? aside from another 258? I don't think they used them on Dodge Caravans?
Yeah, the Caravans are electric. The engine is in line with the front axle, so a crank-driven one is impossible.

Also, I didn't know about electric fans killing HP! Thanks for that info.
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post #8 of (permalink) Old 05-16-2007, 12:33 AM
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FiveSpeedWrangler:
To move air takes energy. It maybe electric energy, or mechanical but in the end the engine needs to provide the energy. Either directly using the mechanical fan or electrically through the alternator.

TiminMB:
I do not know if it made a difference in mileage, but it really helped the time needed for the engine to warm up in the winter, even with cardboard in front of the radiator. They also work great in deep water, I have wadded out and checked with water up to the carb. The fan was windmilling very slowly, I could grab it by hand and stop it from turning. Much better then the fixed fan, throwing water everywhere. One problem is that they do not seem to last well, I have had two clutches fail, both on the tail, which can be a real pain. I plan to make some small angle brackets with holes in them, to bolt to the pulley under the clutch mount bolts. That way if it fails I can use bailing wire to tie the fan blades to the pulley and be good to go.

By the way I have been meaning to thank you for the great writeup you posted years ago on the MC2100 swap. It made my old CJ7 seem like a new Jeep. Thanks.

Wilhelm

I will start using Metric only when the duodecimal system is adopted!!
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post #9 of (permalink) Old 05-16-2007, 09:18 AM Thread Starter
 
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Bandhmo2, the point about quicker warmups in the winter definately appeals to me. I hate the thought of it blowing all the -30 air around under the hood for no good reason. And thanks for the thanks on the MC2100 writeup. I wish I could say I was an innovator in doing so, but its more like I founds bits and pieces of existing information on the swap and wanted to try it for myself. Glad to hear it worked out well for you.
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post #10 of (permalink) Old 05-16-2007, 10:24 AM
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Everyone is correct about the energy aspect....mechanical or electrical, the engine has to put the energy somewhere.

Each one has advantages....mechanical is simple...electric is more flexible....

With mechanical you have the issue of less finger space, more stress on the water pump bearing and even though you have that fan clutch, it does not necessarily free wheel at fwy speeds...if it's a hot day, your doing 60 mph..and the engine is working pretty good...you will be getting a lot of heat off that radiator...even though your moving at 60mph and pushing much more air through the radiator than the fan can pull, that air is hot..hence, the fan clutch locks up....not too much energy savings there....

With electric, it's driven off a temp switch...it does not care how hot the air is...only the water...once your speed gets over about 2030 mph, there is more air going through the radiator than the fan can pull. Even if the fan stays on, the load is almost 0 due to the air flow trying to spin the fan.

In the totality of things, I think electric is better....I have more control over it...it's only draw back is the slight increase in complexity...

Except for the fan it's self, the only real items that can fail are the relay and temp switch. You can solve the relay problem by adding a bypass switch that feeds 12 v straight to the fan. Ask Thor about how nice that feature is....and you can turn off the fan when you go through water....

So...to answer the question...yea, electric will give you better MPG.

AKA DDawg16
84 CJ7, SOA, 5.7LTBI, 4L60E, 35"x12.5, 4.10 gears, F/Det, R/ARB, Full Roll Cage,
D44 Flat top in progress...
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