Electric Fan Application?

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Originally posted by jaymaechtlen
Maybe dumb question, but:
What's wrong with a pusher fan?

True, most factory setups are pullers, but that's not a complete answer...

regards
Jay

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Driving down the road any fan is of little benefit as "ram air flow" is moving through the radiator to carry away the heat removed from the coolant (assuming sufficient grille opening, no debris, sufficient core size, etc). Putting a pusher fan in front of the core is an obstruction to that air flow at speed. The pusher fan may have some benefit at low/no speed as it will keep some air flowing to carry away heat. Mounting the fan, electrical or mechanical, behind the radiator (puller type) has the advantage of not restricting ram air at speed, and providing flow at low/no speed. You'll see some shrouds that have "flapper doors" made of "rubber" sheet stock that will open when the ram air effect is in place, and the draw of the fan will keep them closed when the vehicle is stopped or moving slowly.

Some additional thoughts on shrouds. Years ago GM cars had shrouds that were pretty much just a cylinder of metal about an inch larger than the fan (or vice versa depending on your perspective). They made the flow caused by the fan effective only within that circle, and the rest of the core was exposed. Good idea for the ram air flow, but, depending on the cooling demand, could be marginal for low speed. With the advent of A/C becoming nearly standard equipment, that type of system wouldn't work anymore. That's why a "proper" shroud is now considered to be one that covers the entire core surface, and the largest possible fan (s) used to draw the most air through. Of course cfm is important too as not all 16" (for example) fans are equal. There are other factors too, not just core size, # rows of tubes, core material. There's also how well the engine compartment vents (all that rammed or pulled air needs to get out), and how the engine is set up (bare headers/coated headers, rich or lean, iron/aluminum heads, etc. etc. etc.)

ok-
Now:
all the air that enters the core must also exit it.
Why would it make any difference whether the fan is obstructing the front or the back of the radiator core?
It will still cover the same surface area, right?

OR: does the condition of the air coming off the fan blades make a difference? When in front, the air will no longer be travelling straight into the core, but at some kind of angle coming off of the blades.
When in the back of a radiator core, the fan gets straight-flowing air, and nothing behind it cares WHICH way the air is flowing coming out of the fan?

However, the above explanation/hypothesis only matters when the fan is running, not when it is of and the system is working on ram air.

???
regards
Jay

With an object in front of the radiator the air will "pile up", thus reducing flow. The air being fluid will seek the path of least resistance. This leads to another "theory" in cooling system design. If you look at a factory system there will be some method/effort made to seal around the core support so that all air will be induced to flow through the core, rather than seek another path. Often when folks modify a car they don't take this into consideration and remove "things" (seals, baffles, whatever) giving the air a chance to go over, under, or around the radiator.

A secondary adantage of the shroud on the back is that it creates a venturi effect (admittedly minor) that accelerates the flow of the air away from the core.

I have used both types (push and pull) and the pull works so much better. As a matter of fact, I tested the two simply by putting my hand in front or behind the radiator and the pulling action of the puller fan created a very noticable draft as opposed to the push. It just works that much better.

Don't question it any longer and get the puller type and you'll be happy.

The car I have now was set up with a push type and I'm definitely yanking that and installing a puller.