Two hours later I finished this reply. My apologies for the hijack and may the force be with you while reading.
Still on board after the warning? Ok then, buckle up…here we go!
All the research I found shows that the 20903474 Motor is for the 5.3l Yukon’s and not the 6.2l. Are you sure that is the right number for the application? I couldn’t see GM wasting money putting in a 700W motor for no reason, unless it’s the actual
physics behind their choice that was then swayed or became convoluted when it came time to make a decision on the 6.2l cooling system (I know, I know…you can bust the docs balls later on “another physics reference” - hey I warned you ahead of time).
What I mean by ”actual physics”: It is quite possible the 5 blade needs the 700w motor because it needs to spin faster in order to run as efficient (more low pressure due to more space between each blade) as the 7/9. By increasing the number of blades you effectively decrease the space between the blades and in turn decrease the amount of
low pressure - aka the air that is not being drawn through the cooler/condenser/radiator and pushed by the blades towards your engine. If the fan has a bigger overall diameter, or thicker fan blades, this idea goes out the window, because in this case the impeller used to rotate the fan would need to be larger. Although, this still does not mean that a fan with more blades will have more airflow, only that it will have a higher energy consumption and make less auditory noise.
If the fan was a
push style instead of a
pull style setup, the fan(s) would run on high nearly full-time. This is because the air being moved by the blades would constantly fight against [not only] the static pressure of the vehicles cooling components, but also the resistant pressure of the incoming headwind while driving; plus while at idle they would be on due to ambient air temps/realfeel temps/atmospheric temps and from the engine, trans, tires, road…etc.
Since our vehicles use a pull style setup the fans usually kick on when the vehicle is at idle, slow moving/stop-and-go traffic, or grade increases (esp while towing). Static pressures are the same, but with the pull style you have to add the closed engine bay and engine into account - plus anything that hinders or impedes the outflow of airflow. Also, outside temps obviously play a role, but let’s get back on track.
So, with an increased number of blades using the same size or a similar diameter fan you will only:
-
decrease the sound of the air being moved by decreasing the amount of negative pressure (more blades = less sound / less blades = more sound *think rotor wing aircraft and how much sound a helicopter produces from its blades “chopping” the air - that chop is the negative pressure)
-
increase the high pressure air being moved (relative to the static pressures around it).
-
increase the energy consumption, but not increase the airflow proportionate to the energy consumption *meaning less efficient (which I believe is not what you guys are aiming for correct?).
You’re not trying to put in a bigger alternator, fan blades and a bigger fan motor in just to move
a little more air. Instead, you’re trying to move
VOLUME!, which can only happen if their are less fan blades (
low pressure), or if they are MUCH thicker (usually) and/or if the fan is much larger in diameter overall.
Even with the latter being the case, you shouldn’t need larger fan motors and alternators because the airflow (cfm) would then be higher than that of a smaller fan running at the same RPM. This does not follow the rules or apply to us because as I mentioned earlier, we have SUV’s with large hot engines that are too close to the fans.
To not let this reply get any longer, check out this paper on the subject. I checked their work, the numbers are right but they are also subjective, and unfortunately their conclusions are not realistic to our circumstances. However, the information is solid and might help fill in any blanks left by my ramblings above.
*I want to go on record and state that I am not responsible for any headaches or further confusion caused by trying to understand the equations in this paper - skip over them, I’ve already ensured they are correct.
https://www.tandfonline.com/doi/pdf/10.1080/19942060.2013.11015454
