[DeTomaso] Stock fan output vs. Flex-a-lite

[Scott Couchman]

FWIW.....I spent some time at SEMA talking with after-market radiator and fan suppliers concerning overheating issues I have with my 5.0 Mustang when driving ORR at speeds above 125mph. There was a lot of conflicting information/opinions, but one of the comments that made sense to me was that pusher fans are pushing cool air, while sucker fans are sucking warm air. Cool air is easier/more efficient to push than warm air is to pull.

mikeldrew at aol.com wrote:  
Jack wrote:

We've also found sucker-fans (behind the rad rather than pushers from 
the front) to be much more efficient than
pushers, and another efficiency increase comes when suckers are 
combined with a
full shroud that forces air flow through the entire rad core, not just 
two spots
directly in front of or behind the fans.

>>>It's worth mentioning that this shroud has both advantages and 
disadvantages. It improves the efficiency of the fans at lower speeds, 
but can radically decrease the effectiveness of the radiator at higher 
speeds, because it causes a restriction--the relatively small openings 
prevent air from flowing through and out of the radiator at elevated 
speeds.

Johnny Woods found this out when he installed the Flex-A-Lite unit on 
his Pantera. He routinely drives around France at 150 mph, and he 
found that at triple-digit speeds, his car would start to overheat, but 
it ran fine below 100 mph, which is a classic symptom of an airflow 
problem. He wound up cutting the shroud apart and making an elaborate 
series of trap doors/flaps, which blow open when the pressure inside 
the shroud is greater than that on the outside. At lower speeds, when 
the fan is spinning, it is creating vacuum which sucks the trap doors 
closed. In fact, he may have gotten the idea from me, as this is an 
OEM arrangement used by VW on all their water-cooled cars, and I 
described the mechanism in use on my Sciroccos to him when he asked me 
about his problem.

If you aren't in the habit of cruising at 100+, then it's probably 
never going to be an issue for you, and you can probably get away with, 
and in fact be quite happy with the Flex-A-Lite suckers. Having said 
that, the non-shrouded Spal fans that Wilkinson sells work extremely 
well too, and flow enough air to render a shroud unnecessary. Take 
your pick.

Installing a fan setup with the shroud in front of the radiator is the 
stupidest thing I've ever heard of--yet Flex-A-Lite markets some of 
their fans thusly.

Another point Jack made bears repeating--many fan manufacturers sell 
their fans with a cheesy mounting kit that relies on custom zip-ties 
that pass through the radiator core, to secure it to the radiator. 
This is NOT a good idea, and more than one Pantera owner has found out 
the hard way that road vibration etc. will cause the fans to move 
around on the radiator, and the zip ties act like little saws, slowly 
cutting the radiator apart until it leaks. IF you can find no better 
way to secure it, get a small-diameter aluminum or brass tube, 
carefully feed it through the fins, and then pass the zip ties through 
the tube. That MIGHT prevent a leak--but in my view it's no substitute 
for a proper mounting system, which utilizes brackets which are 
brazed/welded/whatevered to the radiator frame itself, without actually 
touching the fragile core. To me, that alone justifies the added 
expense of buying a package from a Pantera vendor, rather than saving a 
few bucks and ordering the ingredients from Summit etc.

Cheers!

Mike
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