On Sunday, August 31, 2014 3:42:13 PM UTC-4, email@example.com wrote:
Did the Corvair have a hydraulic fan clutch or is it direct drive?
I was raising the point about a hydraulic fan, in which case, the fan
isn't connected directly to the engine and *forced* to an unrealistic
speed that isn't needed. The hydraulic clutch slips and if the load
gets greater, I think it's going to slip more, limiting the top RPM.
If auto fans used such huge horsepower, why do you think the
auto manufacturers the world over were so slow to move to electric
fans? From what I recall, most cars continued to use them into the 90s
Most cars converted over in the 90s, but many still had them past
2000. BMW X5 had it until 2008. Why do some SUVs, many light trucks still
use them? If they use 10, 20, 40 hp why didn't the auto makers yank
them all out in the 80s? I think it only takes around 50hp to keep
a car moving at 55mph. 5, 10, 14 hp is HUGE compared to that. And
most of them had auxilliary electric fans in the cars already. Yet
all these auto manufactuers the world over, with all their dynos,
wind tunnels and far more sophisticated test methods than any hot rodder,
no one stood up at a meeting and said I can take MPG from 15 to 25
by removing the fan? We can meet CAFE standards for the next 20 years
without spending $5bil to make all kinds of little changes that add
up to 1mpg? It just seems to me if it was that big of a hog
in typical cars, you would have seen a sudden converion circa 1980.
Instead it went on 20 years and in some cases is still going on today?
That part just doesn't compute for me.
It probably cost a couple of dollars more for the electric motor than a fan.
Gas prices were not that bad. Most of the time the engine was running at
2000 rpm or less , so at slow speeds the fan was not taking that much HP.
As it go up with the cube of the speed, it mainly sucked up the large HP at
the higher (racing) rpms.
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On Sunday, August 31, 2014 6:23:10 PM UTC-4, Ralph Mowery wrote:
The auto manufacturers were all desperately spending billions to increase
MPG to meet CAFE standards that went into effect in the 70s. They were
retooling all kinds of stuff, switching to plastic, shaving ounces off of
metal parts. So, it's still hard for me to fathom that many cars still had
mechanical fans into the 90s and even past 2000 if they used a significant
share of HP.
Most of the time the engine was running at
I agree. That's why I've asked about
whether those tests, numbers etc were done with say a 1990s era hydraulic
clutch, or just a fixed fan with no clutch. I would think there would be
a big difference between the two, because the one with a clutch probably
won't go to 4500 where the power escalates. It has slip and if it gets
harder to turn, you would think it would slip more and not go up as much
in speed. It might max out at some much lower speed. Which is kind of
what I recall working around cars. If you revved the engine with the
hood up, you noticed a pickup in fan speed, but it doesn't seeem to me
like it went from 800 RPM to 4500, ie 6X.
On Sun, 31 Aug 2014 06:01:00 -0700 (PDT), trader_4
From what I read of fluid fan clutches they don't let the fan spin any
faster than about 2300 rpm. So that's going to limit the maximum HP
draw. The 40 hp does seem like a lot but remember, this is at 4500
rpm so that mechanical fan is really spinning. And if as you say,
things go up cubed instead of squared, a direct coupled fan of 5 HP
at 1500 is going to be pulling a heck of a lot of HP at 4500.
Just as a reference point, I read from a semi-authoritative source
that the old heavy duty GM Turbo-Hydromatic 400 could take as much as
40 hp off the engine output on a dyno. So imagine the drain on power
of an older car with the TH400 and a hd mechanical fan when it's at
On Sun, 31 Aug 2014 14:32:41 -0700 (PDT), trader_4
Trader, keep in mind that the 40 hp was for a super hd mechanical
direct connect fan. Almost NO automakers used such a fan on typical
cars. These guys were using it to see what the most hp drain might
be. Back in the day almost all non ac cars just had a crappy stamped
steel almost flat 4 blade fan if a 6 and a crappy 5 blade fan if a v8.
If they had AC they usually had either a fluid clutch (GM and
Chrysler) or a flex fan (Ford). And except for when you were "gunning
it" to pass or the stop light grand prix these engines were only
running 1800 to 2500 rpm unless you got a performance axle ratio. So
they might only be pulling 5 - 8 hp most of the time.
On Sunday, August 31, 2014 8:11:58 PM UTC-4, Ashton Crusher wrote:
That was kind of one of my points, that the "test" numbers some are
using to justify these high fan HP are not representative of the type
of fan under discussion, ie one in 2000 - 2007 BMW X5 or similar. It
sounds like some of the companies selling electric fans and the proponents
of them may have glommed on to those numbers. The problem is, I haven't
seen any test numbers for say a 90s era car or current SUV, light truck that
use modern hydraulic clutch fans.
The only great value I see to electric fans over mechanical with
clutch is that they can run at MAX when the car is idling. For some
cars that's important, for others it's not. On my 69 firebird I have
an electric fan off a big Lincoln. It just runs hot and this works
better overall then either the original style fan and clutch or a flex
One of the things I think some people are failing to recognize in
their comparisons of electric industrial fans versus these car fans is
the industrial fans are not pulling the air thru a honeycomb of a
radiator. There is a fair amount of resistance to pulling the air
thru that and just as the hp required for the fan being cubed as speed
increases, I'm pretty sure the resistance of drawing air thru a
honeycomb increases faster then a linear rate as the CFM's increase as
the fan speed increases.
A mechanical fan with clutch is always turning - always.
There is no free-wheeling.
The electrics in my car hardly ever go on in the winter.
The only reason I can think of for using a mechanical fan
is the auto manufacturer didn't want to change engine controls,
or electrics couldn't keep it cool enough.
I don't know how much HP the fan uses.
The dyno results I've run across are all over the place.
But there's a HP difference in favor of electrics.
I never had either type fail.
On Tuesday, September 2, 2014 7:22:00 PM UTC-4, Ashton Crusher wrote:
I agree with Vic and I think you do too. An electric fan can be controlled
so that it only runs when necessary, which is only a fraction of the time.
I've seen people claiming they have taken out mechanical fans and not replaced
them with anything and the vehicle doesn't overheat. I for sure wouldn't do
that, but when the car is moving at road speed, winter, etc, the fan isn't
needed and the electric can stay off. I also agree that another advantage is
that the elec fan can run at max speed when the car is idling. I never
doubted that an electric fan could have some advantage, only questioning,
like you, how many HP it really adds up to.
Now for an example of how you can go too far, here's what BMW does with
their existing auxiliary fan on the E53 series X5. Instead of making it a
simple on/off fan, they made it variable speed, with the variable speed
electronics in the fan motor. Great idea. Put electronics in a fan that's
in one of the worst possible spots, ie heat, road spray, etc. And then
they send it a PWM control signal. So now, if the fan isn't working, there
is no easy way to diagnose it. You can't just put 12V on it, see if it spins.
Neither can you put a VOM on the incoming wires to see if the system is
telling it to spin. And for a final good measure, they supplied it with 12V
all the time. One of the failure modes is for the miracle fan to create
a parasitic draw that drains the battery overnight. It's great for the BMW
dealership though, those fans are $500 and a couple hours labor to put in.
Well, you can call that luck. I've had customers' clutches sieze up -
so they run full tilt all the tome. I've had then fail that they don't
drive and overheat. I;ve had them get so sloppy the fan came off and
went through the rad..
I've had flex fan blades crack and come apart. I've had rivetted fixed
pitch solid fans loose blades (and come through the hood).
And I've had electric fans get so stiff they've burned out the
protection fusible link, I've had them totally sieze, and I've haf
them get so sloppy the rotor ground away the magnets, as well as
having them just plain burn out. I've also seen them get so hot they
melted the plastic blade right off at the hub.
That said, Istill prefer the electric fan. (after 46 years experience
as a mechanic)
I put a new fan clutch in my Aerostar a few months ago when I replaced
the radiator. Worked fine for a few weeks, then started overheating
when idling on a hot day - not every time, just when I'm not watching
the gauge. Sure enough, it was failing already. It's such a bear to
swap it out, I wouldn't mind putting an electric fan in there this
time. I can see wiring fun though. But I wouldn't mind if it ran all
No problem wiring it at all. power wire direct from battery positive,
through fuse to relay to motor, and to ground. a temp switch on the
rop rad hose if you can't find a place to thread one in (they make
them for this purpose) and run power from switched ignition to the
relay coil, and from the relay coil to the switch and to ground. Less
than 10 feet of wire in total will do the job. You really do NOT want
it running all the time. You can connect a second feed to the
relayelay, to run the fan when the AC is on (or add a second fan
controlled by the AC)
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