The issue of aluminum or stainless steel blades, in my case years ago, is that the stainless steel blades flex and flatten out at higher engine rpms. When the forward motion of the vehicle is supposed to push air through the radiator and a cooling fan is allegedly not needed. In which case the blades should be aluminum (non-flex) and run by a working fan clutch item. When the fan clutch kicks in and out is key, though.
The observed issue with a flex fan is that during high ambient temps, wind or no wind, as the engine rpm increases (which would draw more air through the radiator due to elevated engine rpm), the flex fan blades "flex" and flatten out significantly, which is visible. Initially, I was pleased that my then-new '77 Camaro 305 2bbl came with a flex fan. "No more fan clutches", I thought. But in the HOT summer of 1980, a few years later, with the factory 195 degree F thermostat and well less than 60K miles, the flex fan would only cool the engine down a certain degree, to 210 degrees F, in the shade inside a large open parking garage and with the car aimed into the 20mph wind. I was not terribly impressed as I felt a clutch fan fixed blade fan set0up would have done better AND I could hear it working.
Ford initially used factory flex fans in the later 1960s to alleged good success. In about 1975, I needed a new fan clutch on our '66 Newport 383 2bbl, but did not really want to spend the money for one . . . at that time. I used a shadetree "fix" by using a larger Phillips-head screwdriver to "imprint" the metal front of the fan clutch, where the silicone fluid is located, to increase the fluid pressure and make the clutch lock-up again. My advisor in this case had gone farther and used the "imprint" to actually stake the innards of the clutch together, making them solid, which I did not desire to do. With the higher fluid pressure, the fan on the Chrysler would unlock later, which I felt was good, but as a short-term fix.
In the mean time, I researched (as best I could in those "analog networking" days) and decided on a Flex-A-Lite stainless steel flex fan. A quality product from a known-quality company. Got all of the spacers to correctly position the fan in the factory fan shroud. It worked great and moved massive amounts of air . . . at a cost in added underhood noise. It was in the middle of TX July and 100 degree F temps. I was driving about 1.3 hours one way to work and back. Once the engine got past about 2000rpm on the freeway, the fan sounded like it was an airplane getting ready for a takeoff which just kept building. I even looked for a possible fuel economy increase from all of the perceived air the fan was pulling through the radiator, but that increase never happened. How well did it work? After that 1hr+ freeway trip, in 100 degree F temps, I could get home, raised the hood, not be bowled-over with underhood head, and grab the air cleaner and NOT have to quickly set it down as it was only about 80 degrees F or so warm. I was impressed with that fact, but the related sounds made it sound like a fixed blade fan on a hot rod with a 4.56 rear axle rather than the 2.76 it had.
Certainly, the Flex-A-Lite product was excellent in what it was doing and certainly looked more at-home than the green flberglass "right angle blade" fans many hot rodders were using back then. But the sounds were not good. I did more research on fan clutches and where to buy them at a good price and returned to that orientation. I removed all of the Flex-A-Lite items and returned them to the speed shop I got them from. All was quiet again and cooling was to Chrysler factory specs, again.
On the Camaro, I changed the orig flex fan with a OEM GM replacement item, suspecting the orig item's blades had gotten weak and were flattening out too soon. The new one did no better, so I started to research fan clutch set-ups for that OEM application. I ended up with a Police Impala set-up and it's still working great. So both of the factory flex fans are laying on a shelf in my shop.
As I had already gone to a 3-core Modine radiator on the Camaro, which came with a 2-core HD radiator with the factory a/c, the coolant temps would still rise past the 180 degree F thermostat's normal running temps. My theory was that at the 2000rpm cruise (55mph speed limit back then), the fan blades were flattened out as they should, but also could be blocking air flow through the radiator at the same time. Whereas the factory fan clutch would freewheel when air flow through the radiator would turn them rather than needing engine rpm to turn them. Hence, no possible restriction to air flow through the radiator at any vehicle speed.
On some of our Chevy customer's 3/4 ton pickups, in hot weather, while towing, they'd come in with the complaint that their vehicles were downshifting when running down the Interstate. What they were hearing was the fan clutch cutting in and out, not the transmission downshifting. When it was explained and they understood what was happening, after checking for any possible malfunctions, including a coolant level check, they were happy to know what was happening and why, continuing on their trip.
This is "the long answer" to the difference in aluminum or stainless steel fan blades and which is better. Adding an electric pusher fan to the factory-style set-up can be needed in certain locales, as Gerald has done. Staging the electric fan's operation IS important, to have it come in before it's needed rather than trying to cool a hot situation that is already too hot. One issue with electric fans is getting them wire-in correctly and their added electric load to a 60amp (approx) charging system. Although I recall no issues with "factory a/c" capacity alternators back then from those who installed them in their factory a/c vehicles. BTAIM
Just some of my experiences, back then,
CBODY67
