Why a massive radiator fan in pickup?
Why a massive radiator fan in pickup?
(OP)
I get useful repair information for my 20 year old Ford pickup from an F150 forum. New Ford pickups (Chevy pickups as well) drop clutch fan and come with electrical radiator fan, and some forum members adopt the setup in their older vehicle. According to the tribal knowledge there, the dual fan setup draws as much as 60 A (not surge current). 60A x 14V = more than 1 HP. I have a shop fan on a 1/2 HP motor and know how much air it blows. I cannot imagine how much air a 1 HP fan can blow.
Assuming a car radiator is designed to provide sufficient cooling from natural air flow while the car is moving, electrical fan seems to kick in only when car is stopped at traffic lights. Someone used a small fan from a Toyota sedan (after removing clutch fan) without any heat related issue. What is the basis of installing a massive cooling fan?
Assuming a car radiator is designed to provide sufficient cooling from natural air flow while the car is moving, electrical fan seems to kick in only when car is stopped at traffic lights. Someone used a small fan from a Toyota sedan (after removing clutch fan) without any heat related issue. What is the basis of installing a massive cooling fan?





RE: Why a massive radiator fan in pickup?
TTFN (ta ta for now)
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RE: Why a massive radiator fan in pickup?
A stock cooling fan on an engine consumed nearly 30hp at 5500rpm, you can see the power drain at anything over 3000rpm.
It even cuts off almost 20 lb-ft of torque at 3800rpm.
This why electric fans are the way to go.
Why are they large? Because of the resistance of the radiator and air flow required.
Think of worst case, 115F outside temp, long grade, low forward speed, full throttle.
That is a lot of cooling load.
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P.E. Metallurgy, Plymouth Tube
RE: Why a massive radiator fan in pickup?
"Someone used a small fan from a Toyota sedan (after removing clutch fan) without any heat related issue."
And did they test it like the manufacturer did? No, of course not.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Why a massive radiator fan in pickup?
(1) The cooling fan, no matter how it is driven, including the old mechanically driven ones, has to pull enough air through the radiator with the engine idling with the transmission in "drive" and the air conditioning on full blast in summer in Arizona. That is probably the worst-case condition, or close to it.
(2) The old school mechanically driven fans were no exception to that requirement, but if they were a fixed drive ratio to the engine, they of course draw much more air than the engine probably needs when the engine is running under load.
(3) When the engine is actually running under load, the truck is generally moving through the air, and probably no longer needs fan operation at all.
(4) The power taken to operate a fixed-geometry fan varies with the 3rd power (cube) of the speed of the fan. If it pulled 30 hp at 5500 engine rpm then it uses 0.06 horsepower (46 watts, just over 3 amps on a charging circuit that runs at 14 volts) at 700 engine rpm. Of course the electric motor isn't 100% efficient and we're making some simplifying assumptions so it might be more than this in reality.
(5) That fan might not necessarily have fixed geometry and it might not necessarily have a fixed drive ratio to the engine. Fan blades intentionally designed to flex under load, and mechanical/thermostatic fan clutches that partially disengage at higher engine speed, might mean the real power vs RPM relationship isn't the simple cubed relationship described above.
(6) The electric fan in my VW wasn't a fixed-speed fan. It has some sort of speed control in it (probably pulse-width modulation of its power supply) and the ECU controls the fan speed in response to some strategy that the manufacturer has presumably thought about to minimize the noise and power consumption.
You can debunk the 60-amp "tribal knowledge" rumor very easily. Find the fuse that controls the power supply to the fan, and find out how big that fuse is. 60 amps? No way.
RE: Why a massive radiator fan in pickup?
I have a motorcycle with an undersized cooling fan like that, which only covers a corner of the radiator. I pretty much can't ride it in traffic.
RE: Why a massive radiator fan in pickup?
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RE: Why a massive radiator fan in pickup?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Why a massive radiator fan in pickup?
I look at some online and couldn't find any that actually drew more than 25A
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P.E. Metallurgy, Plymouth Tube
RE: Why a massive radiator fan in pickup?
what all this means is that regulating a cooling system can be quite complicated and that depending on engine design, engine load, ambient temperature and airflow through the radiator all play a role and that the cooling capacity required not simply varies with engine load but also with the momentarily possible heat dissipation through the radiator. when after prolonged high speed driving you end up in a traffic jam or at a traffic light there still be quite a large amount of heat transfer from the engine hardware to the cooling fluid, although the cooling capacity is virtually non existent due to the fact that there is no airflow at all....a situation possibly worse then when lugging up a hill with a heavy trailer in a ambient temperature of 40 degrees C....
from all this it can be seen that using a fixed fan all the time is a waste of energy - what is needed is a controlled fan that is able to sustain sufficient airflow even when standing still when the engine just ran on full power. the cause of this is the fact that heat produced is not under all conditions in sync with the engine load and the cooling capacity of the system.
RE: Why a massive radiator fan in pickup?
I have yet to see a fan system that requires 60A when operating. 35-40A is more typical. Having a 60A fuse pretty much proves that fan don't draw 60A when operating.
RE: Why a massive radiator fan in pickup?
RE: Why a massive radiator fan in pickup?
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P.E. Metallurgy, Plymouth Tube
RE: Why a massive radiator fan in pickup?
RE: Why a massive radiator fan in pickup?
I got curious myself and checked the owner manual of 2010 Ford pickup. Two electrical fan relays, 50A x2 with max tow package, 40A x2 without. I commonly see 30A x2 fuses running 8A x2 fans in sedans. So tribal knowledge goes down the drain.
Thank you again.
RE: Why a massive radiator fan in pickup?
RE: Why a massive radiator fan in pickup?
RE: Why a massive radiator fan in pickup?
Essentially a high load for substantial periods of time - easily 30 minutes plus.
Effective speed of outside air into the radiator = pretty slow!
It's for those cases the extra heavy duty packages are made.
Jay Maechtlen
http://www.laserpubs.com/techcomm