Electric vs. belt driven cooling fan

[user removed]

Nissan still used a clutch fan on the Z cars, and probably on some of their trucks (not sure about the trucks).

One thing to consider on the clutch fan is when it is not needed the airflow over the fan could actually reduce the load on the engine to drive the water pump amd the fan, to the point where there might not be any losses at higher speeds (speculation).

I have seen cars driven with broken water pump belts, where the clutch fan was actually providing enough coolant circulation to keep the engine cool. One time on my Z car the water pump belt broke and I limped home using pulse and engine off glide to get 6 miles back to my shop to replace the belt. When I got there the coolant temperature was actually lower than normal.

The clutch fans are controlled by a valve actuated by the small bimetallic spring on the front of the fan, which changes the valve restriction inside the fluid coupling depending on the temperature of the air flowing through the radiator.

I used to demonstrate to customers when their (clutch fans) were worn out by wrapping my hand in a shop rag and stopping the fan blades from spinning and actually spinning them backwards while the engine was running (definitely not recommended).

When they were worn out the customer complaint was overheating at idle.

On a lot of cars, like my 95 Riveria the radiator is angled at about 45 degrees to the vertical and you almost never heard the electric fans come on. I would attribute this to the fact that the angle of the radiator would allow air flow to increase when the vehicle was not moving and reduce the necessity for any fan operation.

I never heard of the electric fan creating electrical current from the air moving across it and turning the blades, making it a generator. Thats neat. I wonder if it actually happens on a regular installation, but I doubt it.

regards
Mech

[jtgh]

there sure are lots of speculation and dreaming here, that is for sure.
a brush motor and a generator are one in the same, cept the brush timing
is set to optimize one or the other , on some air craft, they are both in one.
a starter and a generator , same unit ,with special dual brush arrangement.\
(or similar trick)

your fan clutch test method SHOULD never be repeated , a bad idea if ever there was. Why do that?. wow.!

The FSM of each car explains how to do it with out taking any risk.
this one does well.
Saturday Mechanic - Fan Clutch Replacement - Popular Mechanics

with hand move fan , engine off ,cold, the fan must fell like a knife in natural room temp. butter. if it feels seized to the pump , it is.

NOW start the motor , cold.
and then strobe light (a tool) the fan hub and then the pump pulley.
note the huge diffr in rpm at idle and 2000 rpm. a the 2 points. That is the slip.
next ,follow the above link for the hot test.

most ppl that report huge MPG , gains.
are:
1: dont know how to do it. ( maybe 10000 posts here like that)
2: or the fan hub was bad, why on earth compare something good to something new and good.

google #1 and find out how to do it accurately, it's NOT easy.

averaging , is one way.
same driver, same road, same weather, same every thing.
in science this is called holding the constants and changing only one variable.
control the variables or its all just for fun and is useless.


one more link
Fan Clutch Testing: How To Test A Cooling Fan Clutch | Suite101.com


ok some fan clutches have a spring trap. (opens and closes at a specific heat thru rad) [ bi-metal spring is only one type ]
other fan clutches have a thick Silicone grease inside that gets hard when hot (feels like butter at room temp)
buy a strobe light- tachometer and strobe your fan and learn what it really does. It slips like crazy when cold and then trips on , on hot days , at a red light.

YMMV. really. testing MPG below 2-3mpg is no simple matter.
in fact this is the natural background error, in the best of conditions.
reporting gains inside this range, requires publishing your study and proving all variables were controlled.
as each car has differences and conditions of repair.


if you don't understand it? , take it apart and behold, see what it really is.

But, I still like a flex fan. with the nice curved blades.

I hope my directions and ideas are well received.
All my life , I've fought to kill measurement errors.

otherwise, it's all for nothing.

[Frank Lee]

I would sure think flex fans are more lossy than electric.

Why?

Flex = always turning

Electric = very seldom on.

OK Maybe in Death Valley the flex could be better.

[jtgh]

i never said one is better than the other, just pointing out facts few take in to consideration

• Electric conversion losses are the worst. (double conversion)
• noise
• heat.
• cost
• reliability (complexity is almost never the best solution )
  
  

the flex fan uses little energy ,
but does waste some in very cold climates, because at idle it is not needed
in prudhoe bay.

your choice will always be personal. Floating your own boat....?
I just want to give choices.

many ppl have bad clutches and don't even know it.
or dont know how to test it , or have wrong assumptions of how it really works. ( it just slips most the time)


Best post , for me?
saving motor with broken fan belt. fan made pump spin just enough to save the motor. Chock one up ,for a real fan.
never happened to me i do real PM's on cars. (since 65) Gatorbelts ! Rule.
retired yesterday .

[Frank Lee]

Aside from the pickups and classics, who even has a fan clutch?

[jtgh]

do the math on the Alternator in series with the losses on the electric brush motor.
they are both very wasteful, and in series they are pathetic.
start with a drop of gasoline can work that to the spinning blade (you will not err)

if your car is in Arizona and you drive in bumper to bumper traffic. for hours.
it is ,in fact ,wasting way more energy, then a simple direct drive flex fan.

so consider where you live too. and driving predominance's.

but thinking one is better than another , well that depends.
for MPG , then one that works best is the one that works the least.
and for many , its working full time all summer long.

all engineering is a compromise.

cheers

[Frank Lee]

Of course the electric system has more built in efficiencies...

UNTIL you consider the duty cycle.

[user removed]

Originally Posted by jtgh

Best post , for me?
saving motor with broken fan belt. fan made pump spin just enough to save the motor. Chock one up ,for a real fan.
never happened to me i do real PM's on cars. (since 65) Gatorbelts ! Rule.
retired yesterday .

The belt was one month old and broke at the splice, brand new Nissan part.

Seems a little arrogant to ASSUME someone else does not do PMs.

Maybe your boat has a few leaks you have not discovered.

Spinning a fan blade backwards was an effective demonstration to a customer, very convincing to those who had been jerked around by other unscrupulous mechanics, many who recommended all kinds of PM that had nothing to do with solving their problems.

Kind of an admission fee to their little world of "I am the only really good mechanic on the planet" syndrome.

Maybe a different customer philosophy, but PM can be done by any amateur, while real diagnosis and repair of the cause of the problem is the test of 30 years without a summons to appear to explain your procedures.

No assumptions in this post, eh?

regards
Mech

[dremd]

Again all depends on the run time / run speed / conditions you operate in.

If you are a Las Vegas cab driver in the summer the Engine drive will be more efficient.
If your cooling fans run so rarely that you can't tell (until it hits 95F) when they fail (ME) the the electric will be much more efficient.

[dremd]

Originally Posted by jtgh

[*]Electric conversion losses are the worst. (double conversion)

I'm not sure about that, ever notice how many cooling fins are on a belt drive fan clutch? Even with all of those fins and high airflow it still gets pretty darn hot. I'm not sure about this one, but if I had to guess it would be similar. Now if you could do an on/ off clutch we'd have a solution.

Originally Posted by jtgh

[*]noise

Depends on the fan both ways. I've had belt driven fans that were stupid loud, and I've seen electric fans that were stupid loud.

Originally Posted by jtgh

[*]heat.

Not sure what you are talking about here.

Originally Posted by jtgh

[*]cost

Cost is going to depend on the application, but since most cars have E-Fans to begin with, I'd say that the E-fan would win. and if you were designing a system from scratch then E-fan would almost certainly win.
[*]reliability (complexity is almost never the best solution )

Originally Posted by jtgh

the flex fan uses little energy ,

The flex fan is a pig at low RPM's and drains *less* horspower at high RPM's in an attempt to equalualize airflow/ horsepower loss. If your application needs constant airflow then it is a great option, if you drive your car either in stop and go traffic, have short trips (always on waste the most energy at start up) or on the interstate (high airflow regardless) it isn't such a good option.

Originally Posted by jtgh

your choice will always be personal. Floating your own boat....?
I just want to give choices.

Agreed, just use good Data

Originally Posted by jtgh

many ppl have bad clutches and don't even know it.

If they can run their fan slowly/ not at all then they have no reason to have an always on fan. They should either stick with the broken clutch, or run an E-fan with thermostat.

Originally Posted by jtgh

or dont know how to test it , or have wrong assumptions of how it really works. ( it just slips most the time)

If their car doesn't run hot in their application, then it is of no concern to them.

Originally Posted by jtgh

Best post , for me?

What?

Originally Posted by jtgh

saving motor with broken fan belt. fan made pump spin just enough to save the motor. Chock one up ,for a real fan.

One could argue that several ways.
1) If you had reduced the harmonics of the fan you wouldn't have thrown the belt.
2) You should have watched the belt more closely.

Originally Posted by jtgh

never happened to me i do real PM's on cars. (since 65) Gatorbelts ! Rule.
retired yesterday .

What are PM's on cars?

I've run GoodYear Gatobacks before, and they do work very well, particularly with superchargers.