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Radiator fans

How to make improvements to your car.
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bob_drinks_beer
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Radiator fans

Postby bob_drinks_beer » Mon Sep 09, 2013 4:26 pm

Gathering bits and pieces together to change/upgrade my radiator, and getting ready to strip the AC out my Mk1 made me wonder about the fans...
As it is now I like being able to have the "override" of putting the aircon on and having both fans on constantly when in heavy traffic on hot days, just for peace of mind.

I'll probably use two new slimline fans in a new cowl, but I was wondering if there was a more "intelligent" way to use the second fan rather than just have both come on together? Non AC MX5s seem to run ok with just the one fan, so I was thinking of something along the lines of having the second fan come on and off at different temperatures to the standard fan.
I also noticed the fans go off with the ignition, where as other cars I've had the fans have continued on until the temperature had dropped to the cut out level. Would there much point to wiring the fans independantly to the ignition when there's no flow? Esspecially as the MX5 fan switch is near the stat rather than in the radiator.

This might all be unnecessary complication but I like playing and I'd be interested to know what everyone else thought about it :think:
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Re: Radiator fans

Postby Mazda Mender » Mon Sep 09, 2013 9:59 pm

Persoanlly i would loop them together, but it is easy enough to wire it into a switch to just switch it on when you wish to.
M-m
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Re: Radiator fans

Postby binarypunk » Mon Sep 09, 2013 10:08 pm

There is no real need for the fans to stay on after ignition off, as there is no new heat being added - and indeed the water is no longer flowing so only the rad is being cooled. I guess if it is restarted quickly, it will bring the temperature down faster, but that isn't necessarily a good thing.

If you want to have the fans with independent temperature cutoffs it would be possible, using the ECU temp sender and a small comparitor circuit powering a relay or power transistor to ground the fan relay through a different path to the fan switch.
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Re: Radiator fans

Postby Mazda Mender » Mon Sep 09, 2013 10:13 pm

binarypunk wrote:There is no real need for the fans to stay on after ignition off, as there is no new heat being added - and indeed the water is no longer flowing so only the rad is being cooled. I guess if it is restarted quickly, it will bring the temperature down faster, but that isn't necessarily a good thing.

If you want to have the fans with independent temperature cutoffs it would be possible, using the ECU temp sender and a small comparitor circuit powering a relay or power transistor to ground the fan relay through a different path to the fan switch.

I feel a fettle coming on from Jon :whistle:
M-m
The Disclaimer:-
This post is a natural product made from recycled electrons. The slight variations in spelling and grammar enhance its individual character and beauty and in no way are to be considered flaws or defects, the articles/answers/comments are provided for information purposes and they are not intended to substitute informed professional advice, I or mazdamenders.net cannot personally be hold responsible for any damage occurred from following this procedure or any injuries from it. Proceed at your own risk.


Mk 1 Eunos 93 black V.S II 1.8 ,
Mk 2 .1/4 Roadster 99 black & gold V.S 1.8 being rebuilt,
Mk 1 Eunos 90 1.6 (claimed by daughter)
MK 2.1/4 Blue V.S Roadster 1.8 99 ...being rebuilt

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Re: Radiator fans

Postby Risingsun » Mon Sep 09, 2013 10:37 pm

If my memory serves me correctly, after the air-con had been removed from our track car, pushing the air-con button with the heater fan switched to no.1 position, the air-con fan ran for as long as you wanted it to...
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Re: Radiator fans

Postby binarypunk » Mon Sep 09, 2013 11:30 pm

Risingsun wrote:If my memory serves me correctly, after the air-con had been removed from our track car, pushing the air-con button with the heater fan switched to no.1 position, the air-con fan ran for as long as you wanted it to...


Yes this would work for a switching function. With a little rewiring you could bypass the blower switch so the fan wouldn't be required.

Or to do a temperature controlled switch, something along these lines would work...

Fan Comparitor.png
Fan Comparitor.png (6.65 KiB) Viewed 2598 times


Depending on the comparator you use, you will probably need a feedback resistor to add some hysteresis and you may or may not need R2. The BD435 is probably too much, but it needs to handle the relay coil current.
Jon - UK Mk1 1.6 1993 Classic Red

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Re: Radiator fans

Postby bob_drinks_beer » Mon Sep 09, 2013 11:34 pm

mazda-mender wrote:Persoanlly i would loop them together, but it is easy enough to wire it into a switch to just switch it on when you wish to.
M-m

That's probably what I'll do in the end, but I always like to have a think of other options for these things first because I'm awkward lol
binarypunk wrote:There is no real need for the fans to stay on after ignition off, as there is no new heat being added - and indeed the water is no longer flowing so only the rad is being cooled. I guess if it is restarted quickly, it will bring the temperature down faster, but that isn't necessarily a good thing.

If you want to have the fans with independent temperature cutoffs it would be possible, using the ECU temp sender and a small comparitor circuit powering a relay or power transistor to ground the fan relay through a different path to the fan switch.

I was never sure if some fans stay on to prevent a build up of heat in one place after shut down, but as you say there is no flow so its only the rad that would be cooled, and I agree dumping heat too fast isn't good.
You lost me a bit there, I was following until comparitor circuit... :???:
Risingsun wrote:If my memory serves me correctly, after the air-con had been removed from our track car, pushing the air-con button with the heater fan switched to no.1 position, the air-con fan ran for as long as you wanted it to...

That's another option I'm thinking of :handgestures-thumbup:

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