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Discussion Starter #1
I have a big block that has had every element of the cooling system replaced. It doesn't relly have a cooling problem but it does start to creep up around 220 in traffic.
Heres the question-- I need a new fan and I'm trying to decide if I should just replace the fan I have now with a flex fan OR should I get rid of the old pulley fan and just put an electric fan instead?
Also- if you are in favor of the elctric set up, what brand and size of fan would you recommend?
67 Malibu, 454, mild cam, daily driver.
 

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If your car tends to run hot at low speeds such as those encountered in bumper to bumper traffic, but cools down during uninterrupted driving, you are experiencing insufficient airflow across the radiator at lower speeds and the culprit is most likely the fan. My suggestion is to use a clutch type fan with a non-thermal clutch. Make sure you use a NEW clutch as they do go bad and you can't tell it from the outside appearance. One other thing that you might check is the radiator fin count. I once replaced a radiator with one of identical size and capacity, both were in excellent condition,the only difference being that the original had 10 fins per inch and the replacement had 14 fins per inch. The car ran 20 degrees cooler in hot weather with no other changes.
 

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I'd say a good 7 blade clutch fan is hard to beat with the proper shroud. You consider the mech. fan can draw 10 to 15 horsepower, it would be impossible to power an equal electric fan with a 12 volt sys. You may be able to do this in cold weather with an oil cooler and a man. trans but that's probably about it. tom
 

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I agree with the people above. A engine driven clutch fan is the way to go. I'm a Phoenix native, and electric fans don't do the job. I also agree that a rad with a high fin count helps. I also have a engine oil cooler on my Elky. City driving in 110+ degrees, with the AC on, I need all the help I can get. Good Luck.
 

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As Tom3 noted, a mechanical fan consumes a lot of horsepower BUT only at high engine speed. I vote for an electric fan which will do a better job at low speed and extended idle. I'd recommend using at least a 100amp alternator to make enough juice to run the electric fan.

68396
What's a non-thermal fan clutch?
 

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Before you replace the fan test it. With the engine warmed up real good stop the engine, grab the fan and see if it is easy to turn. If it turns easy your thermal clutch is out, replace it. I also like the 7-blade fan with correct shroud and at least a good 4-core radiator for a big block. If I was to install an electric fan it would be for back up and supplement the clutch fan.
 

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First - do you have a shroud???If not I suspect that as the problem.
As above, check the fan clutch. Ultimately I believe a belt drive fan is the way to go.


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If you're already having problems with a mechanical fan an electric will not cool you better. one of my biggest regrets was switching to a 16" derale electric. i ran hot constantly and eventually cracked a head. space your fan no more than 2" from the radiator (this makes a huge difference). if you're in a warm climate run a 1/3 antifreeze to water mix. this will protect a little below freezing and cool much better. of course a quality aluminum radiator will help cool another 10-20 degrees. a buddy of mine uses two 12" electrics in front for "auxilary cooling" when stuck in traffic in the 110 texas summer. good luck!
 

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I've always run the stock 3 core rad, 7 blade clutch fan and shroud and have had no cooling problems even in stop and go traffic. A couple of small electric fans on the front of the rad as well might be a big help in really hot climates. I lost a rad one time when an aluminum flex blade fan shucked its blades. Pontiac had some big stainless bladed flex fans but I don't know how they would stand up to the rpm that many Chevies are capable of. They certainly could move a lot of air at low speed.
 

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I run both an electric fan and water pump driven fan on my 68. The electric fan helps when sitting in traffic in the summer. I have used this combination on several cars for many years. The point I want to stress is I have never had any luck with doing away with the water pump driven fan. An electric fan by itself just won't cut it- use both.
 

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Discussion Starter #11
Now theres some good info! Thanks to all of you for your input -- I think I'm going to get a seven blade clutch fan and see how that holds up. If needed, I will add a small electric fan to the front of the radiator for heavy traffic.
 

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Fred, fan clutches do come in two flavors, thermal and non-thermal. Visually they can be identified by the thermal having a bi-metal spring on the front of the clutch, looks sort of like the spring on a divorced choke. The thermal engages the clutch only when the temp of the air flowing across the clutch is high enough to cause the spring to move a valve inside the clutch which causes it to engage. The non-thermal has no such spring, it stays engaged constantly at lower speeds and is designed to disengage in relation to the speed of the fan, usually about 3000 rpm.
 

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Joshua, If you do go with the clutch fan, stay away from the cheap ones, head for your chevy dealer. Three times the price, but worth every penny.
 

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If you go with an electric fan you will need a really long extension cord or stay close to home.HE HE. Josh go with the clutch fan biggest rad you can fit in,and most important a fan shroud...FRED
 
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is this an automatic with a larger stall speed convertor? they tend to build up much more heat in traffic than stock convertors. had this problem with my stroker motor and solved the problem by using an external trans cooler w/fan located under the car. cruising temperatures stayed the same but dropped 10 degrees in traffic. also do not think 220 is all that bad if the motor makes big power and has large compression its expected.
 

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I run two 12" electric fans mounted on a plenum/shroud behind an aluminum radiator. I chucked the pump-driven fan & clutch after I changed my 6th water pump (short nosed - different brands) on my daily driven 327. One fan runs on the key and the other runs on a 190 degree thermocouple. The make A LOT of noise but work just dandy here in So Cal. Considering the noise - if I were to do it again.......................
 
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