[Kenth]

A freewheeling thermoclutch at highway speed robs zero power, just as an electric fan not running.

Thermoclutch engaged in city traffic robs equal power from engine as an electric fan running. No free lunch.......

Electric fans may be used when space doesn´t allow a thermoclutch.

[Steve C.]

But many tests indicate the fans elec load on the alternator is not all that much, on the one test it indicated about 1 hp. I've read similar testing in Circle Track magazine that sugested similar low figures. And a thermoclutch type had more hp loss. But also the dyno testing was at higher rpm and I assume the on track testing was at speed. So is it differant for city traffic and / or highway crusing ?

[Motor Daddy]

Originally Posted by Kenth

A freewheeling thermoclutch at highway speed robs zero power, just as an electric fan not running.

There is no way the force is zero, no way. An open circuit is ZERO.

Originally Posted by Kenth

Thermoclutch engaged in city traffic robs equal power from engine as an electric fan running. No free lunch.......

Sitting at a light and the fan pulling air through the radiator, If I compare an electric fan and a mechanical fan with the same fan blades, at the same RPM, with the same radiator conditions, same atmospheric pressure, etc etc, the electric fan will be more efficient, it's not even debatable.

[Steve C.]

Opps, I forgot at hwy speed the fans may not be on.

[dmac]

Add in the higher weight of mechanical fans and the extra pulleys, and it starts adding up. Plus the weight added by a bigger shroud than most electrics plus the alt will only be on extra when the electric is on, and the electric will have a finer adjustment for on/off than the clutch so it will be on less than a mechanical. All those add up. As far as not worrying, I have dual fans on seperate circuits, so if one goes out, I've got the other. Throw a belt on a mechanical, and you're cooked. It all just starts adding up, little by little, it isn't just one thing that makes electric better. Then think about just trying to make some minor tuning on a running engine. I'd rather turn the fan off than have the mechanical fan messing up my hair.

[i82much]

Ahh ... it all makes sense now. I always thought "motor daddy" was just a name for a guy who liked "motors." Now I get it - former motorpool sergeant, eh?

So ... do you wear your kevlar when you race?

Sorry, got off-track there.

[Motor Daddy]

Originally Posted by i82much

Ahh ... it all makes sense now. I always thought "motor daddy" was just a name for a guy who liked "motors." Now I get it - former motorpool sergeant, eh?

Motor Sergeant/Instructor. Yup.

[BIGBLUE]

Not sure if anyone mentioned this aspect, but once a car is moving and air is pushing at the BACK of the fan, it will diminish the parasitic HP losses. I would guess that at 60 MPH, a flex or clutch fan is not going to eat up much more HP than an electric. Think about it this way, if you were driving at 60 MPH + all the time you wouldn't even need a fan because of the air moving through the rad, so that same air pressure is going to 'Push' the fan as well, and counterbalance any HP loss.

I believe a fixed dyno test of fan HP losses is of minimum value. The only way to know for sure is to test different fans at the track.

Also, High RPM will cause a fixed fan to eat up much more HP, but if your shifting a 1,000 RPM less than a small block Chevy, you are going to lose MUCH less HP at that RPM. Wind resistance as a negative aerodynamic force increases with the cube of the vehicle speed, and I'm willing to bet the power consumption of a fan follows that somewhat, at least until is stalls and can't move anymore air.

[Motor Daddy]

Where you from, Bigblue? Washington State, perhaps?

[BIGBLUE]

Motor-daddy,

Currently on the east cost, but I fly around sometimes on business.

[Half-Inch Stud]

Seems the PMD motor ALWAYS has the belts upon the Waterpump pulley to run:

the Alternator load.
or the Mech fan load.

Some geometry on belt angles needs to be done before a fella states harsh loads from the slipping MECH fan belt vs the slipping ALT belt.

Yet, I did bust 2 belts at once on an over-rev last time down the track.

[z_bag]

I run a mechanical fan on the street because I think they not only keep the coolant cool, I think they help keep the engine compartment cool. I have 2 friends that use electric fans on BBC's and they run nice and cool coolant temps but in a car cruise on a hot day sitting for periods of time they both boiled their carbs. I think part of that is because the electric fans don't move enough hot air out of the engine compartments. Part of my driveway at home is gravel (farm drive) and I try not to go more than high idle while on the gravel or I will send huge dust clouds out from under the car from the fan.

That said, I will always use a clutch fan on a street driven car. If I were to build a mostly race car I would go electric.

This is just thoughts I came up with and have no real evidence to back it up.

[Joel Koontz]

I have to admit that the cooler engine compartment is something I never considered. I would expect the mechanical fan to keep average underhood temps cooler, because it runs all the time, but, I don't have any issues with my engine compartment being excessively hot.

When the Mark VIII runs it moves a lot of air, probably quite a bit more than a stock M fan does at idle. This keeps the engine compartment from becoming too hot. This may not apply to other E fans that do not move as much air as the Mark VIII fan does.

The fact that his mechanical fan may be blowing up a lot of dust(must be using energy) when my electric fan is probably not even running is more evidence that the electric fan is probably using less energy.

[rohrt]

The Math is simple enough.
1HP = 746Watts
If the Lincoln fan draws 30amps at 13.5 or 14.5Volts this = 405-435Watts or .6Hp

[Half-Inch Stud]

rohrt, that calc is fine, now continue it with a 90% efficient alternator driven (torqued) by a 1.7" radius pulley.
How much TQ at the ALT pulley edge?
How much TQ at the 3" or 4" Crank Pulley edge?
finally how much TQ at the crank?
-------------------------------------------------------------------
My real point is to run a properly tensioned & belted Drivebelt pulley system,
Make so belts prefer to slip the water pump,
Make so belt does not shudder on the Alternator.
MAke so belt does not slip the PS.

Many folks loose the Alternator BOLT, or alternator Field wire due to the alternator slip-chatter under load. Meanwhile the Waterpump slip benefits from the non-clutched Mech fan behaves as a shock damper.
================================================== =====
Cogged V-Belts versus smooth V-Belts make a distinction:
Smooth on Alternator path. I've run cogged on Alt path just fine.
Cogged on PS path.

[Motor Daddy]

Originally Posted by rohrt

The Math is simple enough.
1HP = 746Watts
If the Lincoln fan draws 30amps at 13.5 or 14.5Volts this = 405-435Watts or .6Hp

746 Watts for 1 hour is 746 Watt hours, or .746 KW hours. The electric company bases your bill on KW hours, and you probably pay slightly over 10 cents per 1KW hour.

1 KW hour can be a 1,000 watt draw for an hour, or it can be a 1 watt draw for 1,000 hours. A KW hour tells the total power consumption, but not how it was consumed. Same as HP and torque. 525 HP can be 525 lb-ft of torque at 5252 RPM or 525 HP can be 5252 lb-ft of torque at 525 RPM. The torque and RPM change with the mechanical advantage (distance). It's how a cheater bar works. It's how a teeter totter works.

[george kujanski]

Data point: a 62 A alternator running at 5000RPM requires 3HP to drive, and it is producing 1.16 HP electrical (14volts x 62A). That's only about 39% efficiency due to thermal losses inside the machine and windage due to the cooling fan.

Per the previous post, if a mech fan is compared to an electric fan, same blades and speed, NO WAY is an electric more efficient from a system point of view. The mech is driven directly by the belt whereas the electric is "driven" by the belt also, but throws away over half of the energy to do so.

Obviously, an electric's advantage is you can shut it off when desired, and it allows more flexibility in mounting and packaging in the engine compartment. Electrics became the fan of choice when transversely mounted engines came into use.

A KWH is a measurement of ENERGY, that's what you pay the electric co. for...the amount of energy you use, and yes, it is = to power x time.

George

[Socrates]

I love this debate. I've seen it on every BB of every car or truck make imaginable. Those who have never ran an electric fan are always the ONLY ones to pooo on them and swear by mechanical fans. On the other hand, those who have an elec fan all say they'll never go back to mech.

I love the elec fans I've ran on my Scout, Rallye 350 and GTO. Currently, driving my Scout II daily, the fan is set to come on at 190deg...it NEVER comes on! It's in the 30's-50's here now. In the summer it still only runs occasionally.

I had a thermal clutch mechanical fan on it last week while making a new mount for the electric. The fan ran all the time and the truck NEVER warmed up above 140deg! With the elec back in, I get a warm (warm for a Scout) cabin quickly and the engine is up to temp (~180) and ready to go much faster then with the clutch fan.

There is also a large perceived power increase with an elec fan. A Scout 345 has maybe 150hp on a good day (but tons of low RPM torque, like a Pontiac), so ditching the mech fan could be as much as a 10% increase in HP on this Pig...I'm putting my spare Mark VIII on my 66 GTO as soon as I get an alum radiator. The Mark VIII won't fit the stock radiator, or else it'd be on and the clutch fan would be tossed in the unwanted parts pile...

[Motor Daddy]

Originally Posted by george kujanski

Data point: a 62 A alternator running at 5000RPM requires 3HP to drive, and it is producing 1.16 HP electrical (14volts x 62A). That's only about 39% efficiency due to thermal losses inside the machine and windage due to the cooling fan.

Per the previous post, if a mech fan is compared to an electric fan, same blades and speed, NO WAY is an electric more efficient from a system point of view. The mech is driven directly by the belt whereas the electric is "driven" by the belt also, but throws away over half of the energy to do so.

Obviously, an electric's advantage is you can shut it off when desired, and it allows more flexibility in mounting and packaging in the engine compartment. Electrics became the fan of choice when transversely mounted engines came into use.

A KWH is a measurement of ENERGY, that's what you pay the electric co. for...the amount of energy you use, and yes, it is = to power x time.

George

Are you suggesting the fan draws 62 amps, or that the alternator requires 3 HP to run when fully loaded? Big difference, George.

[Half-Inch Stud]

All well and good to use an Elec fan. Just watch the Alternator overheat for those pesky hot-running engines stuck in traffic. Ask me how I know.

I run a Mech fan and pine for an elec fan again. Reasons:
My engine never gets close to warm in Winter.
Only gets warmed-up on Summer highway.
I like the look of the missing Mech fan; jJust seems respectful of the Water Pump.

I MIGHT re-try the elec fan since my 21year old's half-filled 455 runs fine with elec fan.