I’m not a big fan of direct driven fans, like flex fans, especially on systems designed for clutches. The old direct drive setups had a lower pulley ratio, so the water pump/fan turned slower. The clutch setups are overdriven, the water pump turns faster, but due to the clutch slippage the fan never turns shaft speed. But if a direct drive fan is fitted on a clutch fan setup the fan rpm is way fast, when they fail the shrapnel causes pretty impressive damage, $$$.
… Flex-a-lite IIRC, claims a 5hp (or was it 7?) increase when going to E-fan. ...
Believe all of the advertising hype you want, but where is that HP gain going to come from? If I had to guess a 22R type clutch pulls maybe 2 hp when fully on. The clutch setup is thermostat controlled by sensing the cooler output airflow temp. The thermostat valve is progressive, so most of the time is off/freewheeling or only drawing a fraction of the max possible. When fully on, it's most likely a big load event, so I would be happy to have that much power available.
Since it's not driven of the crank anymore, that hp is freed up. ...
So, where is the power to drive the fan come from? My guess would be from the same belt that drives the fan, the alternator maybe? The belt driven fan has slight friction loss, but is very efficient. So now we power it by taking mechanical power off of the same belt converting to electrical power at what 70% efficiency, run it through connections, switches loosing efficiency, the convert it back to mechanical energy using the motor with about an equal efficiency loss. To drive the same cfm fan electrically will require more belt hp.
There are a set of fan design rules that go something like this:
CFM=RPM, it changes linearly within the fan design range, 1 to 1.
Airflow restriction changes at the square.
HP changes at the cube.
In other words making twice the cfm = twice the rpm, but takes the cube of hp to driven it. It's more complicated than that, like moving that much air drives the restriction number up, so requires more power, etc.
So by removing a fan that has say 2 hp ultimate and replacing it with one that is .25 hp it will pull a fraction of the cfm through a fraction of the restriction. In other words have a fraction of the ultimate cooling capacity.
The belt setup is killer reliable, for an off road rig this is critical for me. Pretty much if the belt is on, the pump/fan turning your good to go. With the electric setup you have a ton more failure modes that will strand you. This is why most off road rigs have belt driven setups.
Water crossings, properly driven with a properly operating clutch fan are no issue. Remember it’s airflow temp controlled, so when some water is splashed into the airflow, it’s rapidly cooled and the clutch freewheels. I have opened the hood of clutched units sitting in water and the belts sling water, but the fan is barely moving, almost stopped with water only 1/4 of the way up the fan.
I’m well aware of the electric fan cars and that they work well, but they are designed to run that way, thinner, higher surface area coolers, etc, that our rigs don’t have. Most are setup that way because of packaging issues, ie the motor is transverse, etc so the pulley isn’t in the right spot to hang a fan. With the proper programming/switching tricks they can be made efficient, but wont have the same ultimate cooling capacity per belt hp.
Yes, an electric fan can be made to work, as long as the cooling load isn’t too high. But if you feel you have excessive cooling capacity and want to recover some of that hp, it’s relatively easy with the clutch setup. Simply change the clutch fluid in it to a thinner fluid and/or change the thermostat so that it comes on later. The only way I would run a primary electric fan on a off road rig would be packaging issue, like a remote radiator or engine swap where there isn’t room, but for me it would be a last resort.
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