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Thread: aftermarket dual fans- slow speed and high speed

  1. #1
    Registered Member WagonCrazy's Avatar
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    aftermarket dual fans- slow speed and high speed

    question:
    I have dual 11 inch fans on my polished alum radiator setup. it all came as a set and is not marked anywhere as to manufacturer...but i think its a mattsons radiator. the fans do NOT say spal on them anwhere, and each one is 2 wires. positive voltage and ground.

    if I wanted to set up the relay wiring to run both fans on "low speed" (from the low temp output signal from the ECU) and the other relay to power both fans at High speed (from the high temp ECU signal), how would I make each fan run at low and high speeds?
    with each fan motor having (only) 2 wires...

    is it as simple as running each with 6 volts for the low speed and 12 volts for the high speed?
    how would I accomplish only 6 volts running to each (if the above assumption is correct)

    LS1 out of a 2002 Camaro, into my restomodded 57 Nomad here...

    Fully wired up already, with low speed ecm signal powering (only) 1 fan to power on at max speed, and a high temp ecm signal powering the other fan to power on at max speed. don't seem to have any fan speed control with this wiring or fan setup... it's all on (full 12 volts) or all off.

    another way of asking is "are fan speeds derived by the # of volts fed to them?"

    another way of asking this is "does a multi speed (capable) fan have more than 2 wires?"

    or

    "do I need an aftermarket fan controller to get dual speed fan setups? something that the stock Camaro ECU doesnt do?
    1957 Nomad- LS1/T56 on C4 chassis
    1959 Fleetside Apache 1/2 ton, shortbed, big window, 327ci.

  2. #2
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    The stock 2002 Camaro has two 11" fans and the ecu and fan wiring gives you two speed operation.

    The way the setup is wired is that when the ecu commands "fan low", the relays output 12 volts to the positive terminal of one of the fans. The negative terminal of that fan is connected to the positive terminal of the second fan, and the second fan's negative terminal is connected to ground. What this does is put 6 volts across each fan, and they both run at half speed. When the ecu commands "fan high", the positive terminal of both fans gets 12 volts and the negative terminal of both fans is grounded.

    This takes 3 relays. I'll see if I can find the wiring diagram on the net and post it, or I'll post a link. If you have the stock wiring harness for the Camaro including the fuse/relay panel, it's all there.

    I would not use an aftermarket fan controller. They are notoriously lacking in reliability, at least in the past. The only catch on using the ecu to control the fans is that the factory temperature settings may be higher than you'd like. To change them, you need to take your car (or ecu) to a tuner and have the settings changed using HPTuners or EFILive, or buy one of those tuning programs for yourself. Thing is, while the factory settings are pretty high, there is no harm done to the engine running that hot, and no harm is done to the tune either.

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  4. #4
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    Another option is to run a fan controller, like the one from Painless. I believe their designation is F5. It has 2 setable temperatures. The first is for 1 fan to come on low speed. That fan speed increases with temperature until setting 2 is reached, when the second fan is turned on and they are both running at max speed. It also has an input to connect to the a/c compressor to turn both fans on max when the a/c is on. I’ve used it on my 56 ls3 and it’s worked well.

  5. #5
    Registered Member WagonCrazy's Avatar
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    Thanks Rick. I think I'm going to have to change my wiring setup from the 2 relay system I have now, to make this run both fans at either low or high (as desired).

    And your point about needing to reset the temp "triggers", yes..I had requested that when I had a guy reflash the stock ECU i'm using, but now that i have the nomad running and have driven it a bit, my gauge reads north of 230 and still no fans turning on. So I dont' think he reset them to the lower temps I requested. I have another friend with an HPTuners package, so we're going to verify the temp settings soon.

    But I can manually ground either of those ECU fan "trigger" wires and make the fans turn on, so I know i have them wired properly.

    so I'll start with redoing this as a 3 relay setup and go from there. I notice from your drawing that one of those relays is a 5 pin style setup. No biggie...just need to redo the underhood relay setup I fabricated that sits in the engine compartment.
    Last edited by WagonCrazy; 12-01-2019 at 01:23 PM.
    1957 Nomad- LS1/T56 on C4 chassis
    1959 Fleetside Apache 1/2 ton, shortbed, big window, 327ci.

  6. #6
    Registered Member WagonCrazy's Avatar
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    Got it all wired up as Rick's suggestion worked.

    started with this existing relay/fuse holder. this is before I did the rewire. Notice there's 1 open "4 pin" hole left there.
    IMG_5719.jpg

    This isn't molded for a typical Bosch 5 pin style relay...so I found the correct 4 pin relay online (fits Toyotas) and then moved/rewired the HORN relay to this 4 pin style.
    IMG_5722.jpg IMG_5721.jpg
    Then reused the open 5 pin slot for what would become the 3rd fan relay.

    Bingo..it's all working as it should.
    IMG_5723.jpg

    Now i just need to confirm what the low temp and high temp settings are (coming from the ECU). 230 seems hot...especially in SoCal summer heat. need them to kick on a bit sooner. maybe 210 or so...
    1957 Nomad- LS1/T56 on C4 chassis
    1959 Fleetside Apache 1/2 ton, shortbed, big window, 327ci.

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    Good show.

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