Ok, Time for me to point out something that's obvious to me but obviously not to everyone else.
From what I have seen over the years OEM type electric fans are MORE prone to failure than mechanical fans.
And by MANY times more prone to failure...
failure can come from many causes because of the complexity of the "system".
a Mechanical fan will turn if the engine is turning UNLESS the engine tosses the drive belt and if it does the water pump won't be turning anyway so you'd have other issues.
Now as for POWER required to turn that fan, the results there are Skewed (probably intentionally) by electric fan manufacturers.
Does it take 5-10hp to turn a mechanical fan at the engine's horsepower peak? Yep, it probably does.
But mostly because in high rpm operation the engine can "overpower" the ability of the thermo-vicsous clutch to slip.
You can literally DESTROY a fan clutch by consistantly spinning
it past it's design speed (but if you are you certainly aren't
concerned about mileage) two hours at 4000rpm with a 2.9 will usually destroy a shiny new fan clutch... (BTDT)
But in Highway cruise mode (at lower rpm) it takes far less power to spin it than the "worst case" figuires given above.
The real benefit to a mechanical fan is it's failure mode.
the fan itself almost never fails but the clutch can, and
while a fan clutch will slip excessively early in the failure
it won't do that for very long before it exibits the typical failure:
Locking solid after which it takes MUCH more power to turn
and is EASILY detected as a "P-47 at takeoff power" noise.
Most cars have electric fans because it is impractical (if not rediculous) to design a mechanically driven fan for a TRANSVERSE engine car.
And many of the cars that still do have longitudinal engines that use electric fans do it because of space or other engineerin considerations.
I applaud the poster above that uses an OEM electric fan from some other vehicle, because the aftermarket fans are utter CRAP by comparison
In the end the "Failure mode" of "Locked-up power drag" but the engine still gets cooled, is preferable to many of us more conservative people than the; "fan simply stops, engine doesn't get cooled" failure mode of the electric fan.
I'll be keeping the clutch fan on my 4.0.
I WILL NOT be designing some Rube Goldberg setup to put
a mechanical fan onto my classic Saab 900 Turbo.
Though I did slightly redesign the relay logic system that controls the fans.
In the factory setup there are two fans, either of which is capable of keeping the engine cool, though in practice the passenger side fan is controlled by the activation of the A/C system.
In my car BOTH fans are controlled by SEPERATE Relays triggered
by SEPERATE temperature switches and the A/C system is set up
to bypass the controlling temp switch.
However that isn't all I did I have a dash mounted switch that
Bypasses the temp switches AND the two fan relays and powers
both fans to on until I manually turn them off with a seperate relay.
And this is on a car that I have literally run for four-five MONTHS at a time with the fans bouncing around in the spare tire well, because from late October to early April the fans simply aren't needed aerodynamic forces drive sufficient air through the radiator to keep the engine cool even in extended Full throttle operation
and therein lies an important difference between cars and trucks.
Most cars with electric fans are designed for "passive" airflow
through the radiator Most trucks aren't.
so putting an electric fan into a car that is designed to survive with NO FAN AT ALL is quite a bit different from removing a NECISSARY mechanical fan from a truck that really NEEDS a powerful fan.
Factory engineers aren't as stupid, nor are factory accountants as stingy, as some here want to make out.
as for the "lets make a fan that's easy to injection mould"?
don't make me laugh. the fans are probably more optimized
for low rpm operation, which hurts them in private dyno testing,
because the factory figuired (correctly IMO) that if the engine was at high rpm for an extended period of time it was PROBABLY moving at sufficient speed for more effective passive airflow.
Remember that factory engineers are saddled with the requirement that they GUESS how somene in the field is going to abuse their best efforts, so they design in a certain ammount of overkill.
I drive a truck and I try to post-design in a bit more "overkill"
Thus I have the higher flow volume water pump (superior impeller design) from a 4.0SOHC, the fan clutch and fan from a 4.0SOHC.
An auto trans radiator (even though I have a manual trans)
the penalties from having too much cooling capacity is a price
I'm more than willing to pay... especially after STILL being able to
drive 1500 miles home after my radiator became partially
plugged internally...
Not to mention that fans and radiators become less efficient at
the 6000-8000ft of elevation at my brother's place than they are at the 500-1000ft when I'm local to my home.
And I actually use my truck to tow.... and that's another thing entirely....
there is no electric fan I'd trust my engine to that can keep up with the heat generated by a 4.0 at 3500rpm dragging a 5000-6000lb trailer up a 7mile long 8% grade.
There is a huge difference between necissary minimums
and needed for "worst case scenario".
you are free to redesign your own truck to your own ideas, it's a free country. But you must sit there and suck it up when you guess wrong, melt your engine and then come to the forum whining about the destruction.
Not believing in Railroad locomotives will not prevent you from getting squashed when you stand on the tracks with your eyes closed and your ears plugged.
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