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Old 04-12-2012, 11:04 AM
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Electric fan thermostat on / off temp?

1967 El Camino 396cid
180 degree thermostat

It has problem overheating while parked. Driving down the highway it'll sit at 180ish all day long. Get stuck in traffic and it starts to climb and doesn't stop. This was with a 6 blade fan and an aluminum radiator. So now I upgraded to dual 13 inch fans to help keep everything cool along with a 140amp alternator.

Seeing as I got dual fans it seems smart to have them come on at different temps as to not shock load the charging system. What on / off temps should I have these set for? On at 190 & 195? Have them both go off at 185?

I'm thinking that I would want the off temp to be something above my 180 degree thermostat that way they will turn off while driving down the highway and aren't needed.

Does it matter really matter if I use Radiator Probes or Threaded Probes? I'm thinking of just using Radiator probes to make the install a little easier and I don't know where I'd install 2 more threaded probes at unless they can all (the 2 controllers and my water temp gauge) run off the same sending unit.


Thank you for your help.

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Old 04-12-2012, 12:35 PM
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You should have your fans set to shut off at least a few degrees above your rated thermostat temp. Otherwise they may turn on and not shut off until you are done driving the car. When I had a set of electric fans I found that most switches usually had a roughly 15 deg spread between cycling on off. I had mine set to cycle on at 205 deg and back off at 190 and had a 180 deg thermostat.

Don't listen to everything you hear about aftermarket electric fans not cooling very well. They do work, you just need the right size fan(s) and expect to see your engine temps cycle up and down as the fans turn on and off while you are at low speeds.

I had dual 12" fans in a mild supercharged 350 in a 72 K5 Blazer.
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Old 04-12-2012, 05:03 PM
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I have used this VSC in a few different applications. It is a soft start variable speed controller so it is easier on the fan and the charging system. It uses a probe in the rad fins which is placed near the hot water inlet area.

http://www.summitracing.com/parts/FLX-33054/?rtype=10

It has an adjustable set point 155 -240 deg and ramps the fan from 60%-100% speed according to the offset between the set point and the actual core temperature. It has a limit of 45 amp load so it may not power both fans, you would need to take an amp draw of two fans running. It will require a signal form the ignition to tell it to shut down after a 30 second delay. It can also accept a signal from a 12v source to force on (100% output) the fans to give a manual over ride. You could wire one fan to it set at 175 and have the other fan activated via your current controller set for 200. If you are running two fans on separate controls have the fan that is closest to the rad outlet start first and shut off last.
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Old 04-13-2012, 07:02 AM
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I have been running the Derale 16789 a Dual fan High-Amperage Adjustable Fan Controller


HOW IT WORKS
The Derale High Amperage Adjustable Dual Fan Controller is designed to
operate two electric fans at different activating temperatures. Fan #1 is
designed to activate at the desired adjusted temperature (150 -240F).
Fan #2 will activate once the vehicle water temperature increases by 10F.
The fans will deactivate 10F below each turn-on temperature.

This unit is designed to control 2 electric fans with a
Maximum Draw of 35 Continuous Amps Per Fan.

Last edited by 65 Imp SS; 04-13-2012 at 07:24 AM.
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Old 04-13-2012, 09:04 AM
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Thanks for the info guys. After looking at all kind of controllers yesterday I just ended up getting two Adjustable Derale Fan Controllers. I looked at the Derale 16789 a Dual fan High-Amperage Adjustable Fan Controller but couldn't find the max amps that it worked with. I also looked at some of the other big amp dual controllers out there.

In the end I just needed something to tell them to turn on. The fans already came with the wire harness and relays.
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Old 04-13-2012, 10:30 AM
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Disregard what I just said. After thinking about how a clean install will look and going to derale's website and seeing that the high amp controller does 35 amps per fan. I changed my order and went with that. I just think it will make for a cleaner install and less stuff to break down.

http://www.summitracing.com/parts/DER-16788/
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Old 04-14-2012, 09:58 AM
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easy and cheap...
i had run out of ports to install a temp sending probe, so i installed it in the lower hose.
short piece of ss 1.5'' exhaust tube, half a 3/8'' ss pipe coupling and a ss #10 screw (for ground wire)
fan only turns on when water out of the radiator is over temp

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Old 04-14-2012, 10:17 AM
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................

Last edited by Blazin72; 04-14-2012 at 10:18 AM. Reason: nevermind... wrong post
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