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Old 05-06-2011, 05:47 PM
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battlerattle battlerattle is offline
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I will try to help throw some light on this situation. Forgive me for being a bit of a noob here, but the electric fan upgrade is something all Jeepers are VERY familar with (we are underpowered no matter what).


First things first. You dont have two radiators. The smaller one in front of the actual radiator is the condensor for the a/c. Though it functions in much the same way, it is technicaly not a radiator.

Now the straight poop. Electric fan size is not as important as air flow volume measured in cubic feet (though there is a strong corolation between the two). You want to flow xxxx cubic feet of air thru the radiator/condensor per minute. You also want to make sure you have two speeds in most cases, a low and high. In the case of my 2010 1500 4x4 (5.7L) it is 1800ft3 for low and 3200ft3 for high.

The low speed is primarily used when the a/c is used to keep a steady flow of air over the condensor when not at speed. This amount should be enough for the system to work without providing too much cooling. Why is this? Primarily because your engine is designed to operate most effeciently at a certain temperature, in my case 165-180*F. Cool too much and you drop below that.

The high speed is designed for when the engine(read as radiator) actually needs to be cooled. The larger volume is needed to cool the greater surface area effeciently and to overcome any heat soak from the a/c condensor (remeber, it is not a radiator though it functions similarly).

As most of you know, durning normal driving on a nice spring day the fan will not be running. The vehicle speed down the road will generally provide suffecient cooling to accomplish most task. But on hot days, when towing, or when sitting in traffic there is not suffecient vehicle speed to push the air thru the radiator. Hence the fan.

A munual/clutch fan is operated by the engine itself via the belt in most cases. This uses available power. Many are surprised how much power is actually needed to turn the fan at the speed necassary. In many cases it can be 10-15+ hp! This is power no longer going to the ground, in essence, making your engine less effecient. The point in switching to an electric fan is to draw the needed power for the fan from the alternator and/or battery vs. directly from the engine. Though the alternator still places a load on the engine and requires a significant amount of hp to turn, it is not nearly as much as the manual/clutch fan. The battery also provide a source of energy for high load usage keeping the alternator from overloading.

Reguardless of which electric fan you use, keep in mind these few requirements. Does the fan flow enough air for my application? Does the fan draw low enough amperage for my current wiring or should I upgrade? How do I want the fan to engage (thermostat or manual)?

Finnaly remeber that electric fans do not like to be submurged. Though not a huge problem in the truck world, we jeepers learned the hard way!


EDIT: This question almost always comes up. Push or pull? it is generally more effecient to pull air through the radiator than to push it through. There are applications where pushing is prefered, but generally not on a street driven vehicle.
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Last edited by battlerattle; 05-06-2011 at 05:53 PM.
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