jaluhn83
Full Access Member
so because you don't feel the significant amount of power loss while hauling or towing heavy uphill,this means the problems reported by so many must be a problem with their trucks and their reports are flawed.it's all in their minds? lol
iv done a lot of research on this.there are many,many idi owners who feel a hefty amount of power drained when the clutch kicks in under load,pulling grades.
Never said they were lying.... but being able to "feel" the fan engagement doesn't necessarily correlate to there being enough of a power drain to cause performance issues. Further, being able to feel it indicates to me a concern in the function of the clutch, since it should not suddenly lock up, but rather should as designed be a progressive increase in fan speed with temperature.
My power estimates come from this site:
http://www.freecalc.com/fansfram.htm
Using 15,000 CFM for a ballpark number I come up with a static discharge pressure of 1.4 in h20, which gives 9.4 hp with a 35% efficiency. 15k CFM would give a ~55 MPH exit velocity from the fan, which seems a fair bit high to me based on ballpark estimates with my truck. (Since I can lock the fan up manually I can check this)
Even using conservative number, I still come up with <10 hp to run the fan. With the rated hp of an idi being 160-175 stock, that means the fan is about 1/16 of the engine full power. While this may be noticeable, it's not going to make that much difference. Now, with a unhealthy engine that's only making say 100hp, then that fraction goes up which may be why some claim to feel it more than others. Likewise, with a turbo that fraction goes down, so it becomes less noticeable. Granted, engine HP will go down with elevation and at lower rpm, but so too will the fan power.
Further, that power is going to something important - keeping the engine cool. With a properly functioning clutch, the fan should only be coming on when the engine gets hot - and also going off when it cools. So if it's coming on it's because the engine is working hard enough to need extra cooling, and if it happens that this is enough to cool it back off again, the clutch should disengage.
I also base this on my experienced with both stock and turboed trucks. My finding has always been that I'm limited my water temp, not EGTs, and the best way to keep the coolant temps down is the stock fan. I have noticed a substantial decrease in coolant temps with the electric clutch and consequently been able to pull a bit harder on hills where I would have had to slow down without the manual clutch. Likewise, with a weak clutch I've seen coolant temps come up very quickly, limiting me substantially.
My point is that seat of the pants feelings may not really capture the entirety of the issue, and that I think the power/mileage loss from a properly working stock fan setup is significantly less than many believe.
That being said, electric fans are certainly a workable option for some. I would suggest the benefit is less than commonly held, and the potential cost in cooling is substantial.