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I changed my stock 4 row radiator for an aluminum 4 row radiator and the car cools a lot better. However, the thermostat gauge does start creeping up again after having driven for a while, and this especially happens when I'm sitting in traffic.

So I'm debating on switching over to an electric fan. I currently have a belt driven fan (and shroud). Any recommendations from the group? If you recommend on going electric, any particular fan you can recommend or cfm that the fan should move?
 

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Creeping up to ......what? Normal operating temperature? Do you have a cheapie aftermarket fan or a good original clutch fan? What pulleys, are they stock and correct or are they underspeed aftermarket pulleys?
 

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When sitting in traffic, the temp gauge needle goes from being right in the middle to 3/4 of the way to the red. On really hot days, even if the car is moving the temp gauge will read above the mid way mark and if the car is stopped, the needle quickly moves up.

I do have a good clutch fan and original shroud and am running March underdrive pulleys
 

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I put an electric fan in also (in between the radiator and the AC core) and kept the mechanical fan and shroud on. I use the electric fan when it starts running hot, like in traffic. I figured that everything will fail from time to time and if the electric fan bites the dust, at least I have the mechanical fan to get me by until I could get a replacement. More of a CYA than anything else.
 

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The under drive pulleys slow down the fan speed for less cooling. They are working great! You might consider reinstalling the stock pulleys until some day when 1 or 2 horsepower is worth less cooling and less alternator charging ability.


When sitting in traffic, the temp gauge needle goes from being right in the middle to 3/4 of the way to the red. On really hot days, even if the car is moving the temp gauge will read above the mid way mark and if the car is stopped, the needle quickly moves up.

I do have a good clutch fan and original shroud and am running March underdrive pulleys
 

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Do electric fans not cool the radiator/engine/coolant as much as the belt driven clutch fan? If I were to decide to switch to electric, has anybody highly recommend for/against it? Any recommended fans or cfm that I should be looking at?
 

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The problem with and underdrive pulley set is that it slows down the water pump pulley (causing not only the pump to not move as much coolant, but it slows down the engine driven fan as well. If you're trying to get that last little bit of high-rpm performance, they're great in that they'll 'save' almost 10hp at 6000rpm. For the street, where you are running at less than 2000rpm most of the time, not so much. The electric fan would be a band-aid solution to a non-existant 'problem'. Just put the stock pulley set back on there and be done with it! Yeah, those March pulleys look cool and all with that underhood 'bling' factor, but they're not what you really want/need for a street engine.

If you're building an all-out race engine in a car that is only raced and not street driven, then go with an electric waterpump or electric waterpump drive and an electric fan so you can cool the engine down between rounds (ie cool all of the the coolant (and therefore the engine) with the engine off).

Don't try to mix the two schools of thought - you and your car will be unhappy.
 

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Discussion Starter #9
Makes sense. Thanks for the insight! This is very helpful!

Anybody want to buy a set of March underdrive pulleys? ;-)
 

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I don't want to take this too off-topic, but I must be missing something here. How does a smaller diameter pulley slow down the water pump? If I remember my physics lessons smaller diameter wheels/pullies rotate more than a larger ones at the same speed...
 

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It's all about the ratio of the pulley diameters. For example an 8" drive (crank) pulley and a 5" water pump pulley have a ratio of 8/5 = 1.6. This means for every single rotation of the crank pulley the water pump pulley will turn 1.6 times - 1000 rpm will spin the water pump 1600 rpm. Underdrive pulleys are designed to reduce this ratio - which eases the load on the engine, but reduces the rpm of the driven pulley. So an under drive pulley set might have a 5" crank pulley and 5" water pump for a ratio of 1:1.
 

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If you reduce the size of the crank driven pulley you reduce the speed of the water pump
and many times they'll increase the size of the alternator pulley by 10-15% or so... That slows down the alternator even more....

I am running a 'underdrive' crank pulley on my 393W since a 'normal' Crown Vic/Marquis spends most of it's time below 2500rpm since they're geezermobiles... My car originally had a 7-1/2" crank pulley. If I run the stock pulley up to 6000 engine rpm, the water pump is churning much to fast, and wasting energy/horsepower. I dropped to the Mustang 5.0 HO 5-1/2" pulley (perfectly fine in a stock 5.0 HO Mustang/T-bird/Mark III/Cougar for cooling) and it 'saves' 15-20 horsepower at upper RPMs (or 10% over the 180hp stock). A 'serious' underdrive pulley, like a 4" crank pulley could save even more... (do the math (Pi x pulley diameter = circumference or belt speed))
 

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I gotta call BS on this one. The amount of horsepower "saved" by the underdrive pulleys cannot exceed the amount of horsepower it takes to drive the alternator and water pump. Those two items take about a horsepower each.

You can't "save" the amount of horsepower it takes to drive the fan. If you change to electric fans you need the same horsepower to equal the same CFM, less 5 - 10% loss from the electrical drive and alternator. So electric fans take more horsepower than a belt driven fan, all other things being equal.

and many times they'll increase the size of the alternator pulley by 10-15% or so... That slows down the alternator even more....

I am running a 'underdrive' crank pulley on my 393W since a 'normal' Crown Vic/Marquis spends most of it's time below 2500rpm since they're geezermobiles... My car originally had a 7-1/2" crank pulley. If I run the stock pulley up to 6000 engine rpm, the water pump is churning much to fast, and wasting energy/horsepower. I dropped to the Mustang 5.0 HO 5-1/2" pulley (perfectly fine in a stock 5.0 HO Mustang/T-bird/Mark III/Cougar for cooling) and it 'saves' 15-20 horsepower at upper RPMs (or 10% over the 180hp stock). A 'serious' underdrive pulley, like a 4" crank pulley could save even more... (do the math (Pi x pulley diameter = circumference or belt speed))
 

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I guess I was showing my ignorance there, I was under the impression that all the pulleys were a smaller diameter, not just select ones. If that's the case then I understand why the water pump would flow slower.
 

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I gotta call BS on this one. The amount of horsepower "saved" by the underdrive pulleys cannot exceed the amount of horsepower it takes to drive the alternator and water pump. Those two items take about a horsepower each.
Royce, I'm not the only one who has seen bigger than 1-2hp gains by going to underdrive pulleys. Read this test for a side-by-side comparison. I'm sure you can find other tests as well... Besides, most cars will also have a power steering pump, and many will have a/c and smog pumps... They'll all be turning slower with an underdrive crank pulley.

Speaking from actual experiences I've come across at the dragstrip, most cars will pick up a tenth or more simply by switching to an underdrive crank pulley. The power increase required to do that is certainly more than 1-2hp!
 
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