The actual truth is there are three factors involving fan performance. None of which are "get a larger/more blade" fan. These factors are assuming, without a shadow of doubt, that you have a "necessary" shroud. "Necessary" if you have a cooling problem and can fit one.
1. Tip of blade to shroud clearance and depth into shroud.
2. Blade pitch angle
3. Distance from Radiator
An upgraded or re-cored radiator, a good water pump and proper thermostat are very important. A rusty clogged system/motor can't be cooled.
Lots of opinions and unsubstantiated BS from automotive electric fan companies.
Topical Tid Bit: Ceiling fans produce less air movement with more blades but are quieter.
A radiator fan is a static pressure style axial fan. Wiki says: Axial fans operate at specific speed i.e., high flow rate and low head and hence adding more blades will restrict the high flow rate required for its operation.
The confusion and false info is caused by hype, misunderstanding the many different types of fans and use requirements. Some users may mix up electric static pressure fans and air flow fans and their blade-to-flow characteristics.
In belt driven auto fans, shrouds and spacing are the trick with 4 blades. The clutches and flex o lite blades have no effect on cooling. They are for more engine power, better gas mileage, possible bearing wear savings at cruise speeds. Ram air cooling takes over at cruise speeds.
