Installing dual electric fans to have fan #1 come on at one temp and fan #2 to come on at a higher temp, do I need to have two independent sensors? Additionally, where do I place these sensors? I already have an aftermarket temp gauge with a sender in the driver's side head and would like to keep that, too.

I have seen water neckets with a sensor boss built in, so that would probably be good for one.

I am trying to avoid buying an electronic controller and was hoping I could just use two relays and two sensors.

I am trying to avoid buying an electronic controller and was hoping I could just use two relays and two sensors.

Just use them.

Bruce: Your now entering the PERFECT STORM. If you buy two sensors, you'll need two controllers. One sensor goes in the water neck on top. I don't have a clue where the other sensor could go. I really don't think your idea of two independent sensors will pan out. Here's my last helping word: Scrap your idea and stop by an Electrical Auto Shop for advice. You'll save alot of time, aggravation and money trying to jury rig something that may not work and remember: Most places will not allow a return of electrical components. Seek some advice ASAP...

Good Luck..!
Bob in CT

Yea...I thought it might be getting a little complicated. What I want is a low/ high type setting, mainly to cut the noise from electric fans. I have read your posts going back a few years and found them to be very helpful.

I was looking at the SPAL unit it looks like it would work ..

http://www.customstreetdesigns.com/4062-FAN-PWM.htm

Yea...I thought it might be getting a little complicated. What I want is a low/ high type setting, mainly to cut the noise from electric fans. I have read your posts going back a few years and found them to be very helpful.

I use two sensors all the time on my two speed fan controllers. All you need is two sensors to close at the temperatures you want, and two relays to control the fans. It's pretty simple. I put one in the water neck and one in the manifold.

If you want to have them kick on at different times (temps), you would have to wire them independent of each other, using two different thermostatic switches. I wouldn't mess with doing that myself, but the theory is still the same and you have to use two relays to do this regardless. I myself like wiring them up to where they are activated by introducing the ground to the circuit, with the therm. switch being what grounds them out, and you can even "piggy back" an in-line toggle switch to the ground circuit to override the thermostatic switch to manually make them come on earlier, or make them stay on longer. Below is the diagrams that come with the spal fan install kit. They just tell you the colors of the wires, but remember, this is nothing more than a standard bosch relay.

According to the diagram, here is what you need to know.

Yellow = #30 on relay
Orange= #86 on relay
Red= #87 on relay
Grey= #85 on relay

Here is the wiring diagram, http://project71.net/skeeveman/Wiring/Electric%20fan%20wiring.jpg

This is THE way to do dual fans IMHO. If you want I will throw up pictures of how I have my relays,fuses, and switch mounted.

If you want to have them kick on at different times (temps), you would have to wire them independent of each other, using two different thermostatic switches. I wouldn't mess with doing that myself, but the theory is still the same and you have to use two relays to do this regardless. I myself like wiring them up to where they are activated by introducing the ground to the circuit, with the therm. switch being what grounds them out, and you can even "piggy back" an in-line toggle switch to the ground circuit to override the thermostatic switch to manually make them come on earlier, or make them stay on longer. Below is the diagrams that come with the spal fan install kit. They just tell you the colors of the wires, but remember, this is nothing more than a standard bosch relay.

According to the diagram, here is what you need to know.

Yellow = #30 on relay
Orange= #86 on relay
Red= #87 on relay
Grey= #85 on relay

Here is the wiring diagram, http://project71.net/skeeveman/Wiring/Electric%20fan%20wiring.jpg

This is THE way to do dual fans IMHO. If you want I will throw up pictures of how I have my relays,fuses, and switch mounted.


I would love to see your set-up in pictures. I looked at your spal diagram and the only thing different that I would have to do is use a second therm switch which has a higher "on" temp....that Spal diagram already uses 2 relays for the dual fans.

If I wanted to put LED indicator lights in cab of car so that I know when each fan comes on, can I piggy back them on the "fan positive" (87 on relay) wire, assuming I use the appropriate resistor?

I guess what I am trying to do is get all the advantages of an electronic controller with out spending the $ on the device which will leave me with the money to buy a nicer radiator.

You can put lights in there that way, and here is a calculator for picking the right resistors. http://ledcalc.com/

Here are the pics. I could pull the battery out and show you the pic there, but it won't help you much because they are all wrapped in harness tape.
http://project71.net/skeeveman/Temp/Fan/

Nothing special to look at, but you can see I kept everything real close to the battery. The only thing I may change later is changing the fuses (they're the inline style in front of the battery), into being fixed to the area next to the relays, which are right behind the battery, mounted on the radiator support.

If I wanted to put LED indicator lights in cab of car so that I know when each fan comes on, can I piggy back them on the "fan positive" (87 on relay) wire, assuming I use the appropriate resistor?

Just buy a 12v LED.

My electric fan over ride switch is invaluable when ridding in classic car parades 160 to 170 max