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Discussion Starter · #1 · (Edited)
I'm going to wire my fan relays to be controlled by my Holley Dominator ECM, which will of course know engine temp.

I read an earlier post Busy made on fan controllers. I have Maradyne fans with relays which I'll switch via the above. I wasn't aware you could run fans at variable speeds. Before someone starts explaining how, is it anything I should even give thought to if I have dual fans and can control them individually?

Thanks,
Charlie
 

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I'm going to wire my fan relays to be controlled by my Holley Dominator ECM, which will of course know engine temp.

Is there any reason any of you think the fans need to continue running after the vehicle has been stopped?

Thanks,
Charlie
I have fans on my BB Vette, and on my 56 wagon. I have them both run a bit after ignition off. The Vette stays warm for a bit, and for both cars, I have can tell that my fans are working. I would have your fans fused, and if you have a timer option, let them run for a little after shutdown. Just my 2 cents worth :anim_25:
 

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There is no reason to run the fan after the engine is shut off unless you can run the water pump too. You'll only be cooling the water in the radiator, not at all in the engine.

As for variable speed, if you have dual fans, many guys including the factory run a two speed system. An arrangement of 3 relays will give you half speed and full speed. I don't know if the Holley will support that, or easily. Factory LS and 95 up LT1 are done that way.
 

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There is no reason to run the fan after the engine is shut off unless you can run the water pump too. You'll only be cooling the water in the radiator, not at all in the engine.
Some cars do this from the factory. There will be some convection. Not a big deal but there is a reason.
 

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my Buicks run after shut off......

There is no reason to run the fan after the engine is shut off unless you can run the water pump too. You'll only be cooling the water in the radiator, not at all in the engine.

As for variable speed, if you have dual fans, many guys including the factory run a two speed system. An arrangement of 3 relays will give you half speed and full speed. I don't know if the Holley will support that, or easily. Factory LS and 95 up LT1 are done that way.
I have wondered why, as no water pump is running,
I know after shut off the temps DO rise, but with out water movement, what is the benefit?
 

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I have wondered why, as no water pump is running,
I know after shut off the temps DO rise, but with out water movement, what is the benefit?
Like I said, there will be some convection and that will remove some heat a little faster from the engine.

Also, in a situation where you shut down the engine and restart after a short time, the water in the radiator would be cooler than it otherwise would have been.

The benefit is probably pretty low but some manufacturers must have thought it was worth doing. The aftermarket Dakota controller allows this feature too so their engineers must have thought it was worth something too.

I have the Dakota and have it set to where the fans will run for 30 seconds after shutoff. It will only occur if the fans were already running at shutdown. I kind of like it that way.

Also since I have dual fans, I used the 3 relay 2-speed setup that was mentioned earlier. It's easy to set up with the Dakota controller because it has a low and high fan output on it and the temperatures are programmable.
 

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Perhaps I should have said good reason.

What do you achieve by running the fan for 30 seconds? The answer is not much. It's a rather short time.

If you've ever done some drag racing where they hot lap you a couple of rounds, you'll realize that the water pump is a big deal on cooling the engine, and that 30 seconds of extra cooling with even the water pump and fan just doesn't do much of anything. To do something quickly you need a stream of cold water on the radiator, or a complete change of coolant.

And even if could cool it down a bit, what does it do for you in the big picture if you're not drag racing?
 

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I'm going to wire my fan relays to be controlled by my Holley Dominator ECM, which will of course know engine temp.

I read an earlier post Busy made on fan controllers. I have Maradyne fans with relays which I'll switch via the above. I wasn't aware you could run fans at variable speeds. Before someone starts explaining how, is it anything I should even give thought to if I have dual fans and can control them individually?

Thanks,
Charlie
Charlie, I have a Spal fan controller that varies the speed of one fan and turns the second fan on when the first reaches the high temp setting. I like it and mine works fine but I think there were problems with some of them and I'm not sure Spal sells it any more, but Painless has a variable speed fan controller. The variable speed controllers need a changing resistance from a temp sensor and I believe the ECM control signals are either on or off. Does the Holly ECM have provisions for 2 different temp settings on different leads? If so, the 2 speed set up would work good with ECM control.
 

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Discussion Starter · #9 ·
Does the Holly ECM have provisions for 2 different temp settings on different leads? If so, the 2 speed set up would work good with ECM control.
Don,

Yes, it does have (2) different Fan setting provisions. I thought the variable speed thing would be interesting, but not necessary.

I don't know what to do with it, but I can output a PWM signal, whatever that is... :)

Here's a snippet from the Holley doc on outputs..

20 - 12v PWM Outputs – Can be configured as PWM or switched 12V outputs. Rated at 2A maximum
16 - Ground PWM Outputs – Can be configured as PWM or switched ground outputs. Rated at 2A maximum

Charlie
 

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PWM is "pulse width modulation", which it the type of signal used by variable speed controller to vary the speed of a motor by electronically turning the voltage to the motor on and off at different rates. But 2 amps is way to little for a fan motor. You would need a high current solid state driver circuit for a fan motor. Your best bet would be to use the 2 speed 3 relay system that Roger1 and others are using and use one switched ECM output for low fan and the other for high fan. ..... http://www.trifive.com/forums/showthread.php?t=62499
You would have to modify the wiring so one relay used the +12 volt signal and the other 2 relays used the ground signal from the ECM.
 
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