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smokeyfan1000
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From a company that produces both types of fans - this is a pretty fair summary of the benefits of each. http://flex-a-lite-blog.com/2010/02/27/which-is-better-–-an-electric-or-belt-driven-fan/
If higher performance and/or greater efficiency is your goal - there's an electric fan/control system that will outperform the stock/heavy mechanical setup and get the job done reliably. It's not debatable. Is it worth it to spend the money on that set up (alternator may also have to be upgraded)? Everyone has to decide that for themselves.
In my case the decision to convert was a part of putting the V8 in as there wasn't room for a mechanical. However, that's not always the case. With a late model 5.0L out of an Explorer/Mountaineer, the accessory package is almost 2" shorter (closer to engine) than the fox body Mustang accessories. Testpoint (on this site) was able to modify the Volvo shroud and uses the mechanical fan off the Explorer in his conversion. Even so, I tried, unsuccessfully, to talk him out of it.
FWIW - almost everything OEM for a quite a while has the ecu controlling the fan - based on coolant sensors that are almost always located where they sense the warmest location of coolant (head, exiting the engine, etc.). My variable speed controller senses the radiator fins near the exit of the radiator (cooled fluid about to re-enter the engine). Previously I had two temp activated switches to control the 2 fans separately - they were both located to sense the warmest temps. You can do it either way -- you just have to know what you're doing.
I read the last 2 paragraphs ...........
Belt-driven Fans
If your vehicle has a belt-driven cooling fan and you?re not making major changes to the engine or cooling system, the simplest thing to do is to keep a belt-driven setup. You can, however, increase your car?s horsepower and fuel economy without giving up cooling capability by using one of our high-performance flex fans.
Since a belt-driven fan increases speed (and airflow) with engine speed, it can move more air at higher engine rpm ? usually above 2,400 rpm ? than an electric fan. Conversely, electric fans move more air than belt-driven fans at engine speeds below 2,400 rpm in typical applications.
One major downside of belt-driven fans is parasitic loss. It simply takes more energy to spin a belt-driven fan than it does to produce the electricity needed for a comparable electric fan.
Here are some of the applications where we would recommend a belt-driven fan. They are better able to pull air through a restrictive cooling unit. If you have a four-core radiator with an inner cooler, air conditioning condenser and transmission cooler stacked in front, a 7-blade flex fan along with a proper-fitting fan shroud will be a great choice for cooling. A belt-driven fan is also a good choice if you are having a cooling problem at higher engine rpm. A lot of off-road vehicles drive at slow speeds with high engine rpm. This can build a lot of heat without any natural airflow through the engine compartment. A thermal clutch fan will make use of the high engine speed to move maximum air.
Which is Right for You?
That?s the key question, right? Here?s our advice: If you are looking for a performance upgrade then the electric fan is for you. Make sure the electric fan covers 70 percent of the radiator core and moves enough airflow for the engine size (a rule of thumb is at least 2,800 cfm for a 5.0L engine). The electric fan would be a cooling solution for vehicles that typically drive at low vehicle speeds with low engine rpm, such as cruising. If you have a 4-core radiator or towing heavy loads then we recommend you stick with a belt driven fan. Finally, if you have a cooling problem, watch this blog for future articles that will help.