Quote:
I can't think of anyone who is dumb enough to spin their engine to 6400 RPM during towing or any overheating situation.
The gas engine redlines @ 6,400... it's totally conceivable that someone could rev the 3.7 to redline with the fan clutch locked.
I have a chevy pickup that's a little under-powered, while towing, I routinely shift it at redline (4.3 automatic, foot to the floor)
Even if "best practice" is to not rev the crap out of your engine while towing, people do it, and engineers have to design things to not fly apart under those conditions....
Think about it, if the 3.7 fan flew apart at redline, then 90% of the liberties out there with 3.7's would have grenaded fan blades.. at some point in the vehicles life, someone is going to put their foot to the floor on a 1 2 shifts, on a hot day, going up a hill, with the AC on, etc etc....
my point is, that all things being equal the 3.7 fans are going to be designed to run at a higher RPM.... which means less air flow at any given rpm....
IE
(BS numbers for a point)
3.7 @ 3,500 rpms = 550 CFM
2.8 @ 2,200 rpms = 550 CFM
take the 3.7 fan, and spin it at 2,200 RPMS: 300 CFM
You guys said it yourself, the CRD fan creates more drag... this isn't due to it's weight, it' due to the amount of air it moves....
The rotating mass of something like a fan in a motor like ours is trivial.... our motors don't change their rpms all that much or all that quickly....
of the energy the fan takes, like 2% is for increasing it's speed (IE, it's mass / inertia) and 98% is for moving the air.....
Something like a flywheel on a street bike that revs to 15K can make a difference, because you need to accelerate it from 6,000 rpms to 15,000 rpms for every gear you pull to redline....
but in our jeeps, our clutches usually only lockup when our engines are at a steady state RPM, usually while towing on the highway,,,,,,
And even if they were to be in lockup while our engine is pulling though the gears..... 3,500 rpms in 2nd, down to 2,300 in third, to pull back up to 3,500 rpms before the 3/4 shift? that's hardly any real change in inertia for the rotating mass....
it also ties into what geordi was talking about with different boats and different props...
for example you can get a 3 blade or a 4 blade prop for a mercruiser stern drive...
I know from experience that given the exact same pitch, the 3 blade prop will have a higher top speed, and the 4 blade prop will have better mid range fuel economy.....
different configurations of blades on a fan / prop give it different RPM and flow and drag characteristics..... long story short, they spent the money for a metal fan on our liberties.... there's got a to be a reason for this.... all things being equal the metal fan will outperform the plastic fan in our application....
now if you don't NEED all the cooling power from the metal fan plus the hayden clutch, that's a different story, but for me, with my 5000lbs boat and 5000lbs travel trailer and the fact I live in a coastal city up against a mountain range, I need all the cooling I can get....
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