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Old 02-16-2008, 02:48 AM   #1 (permalink)
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[CRXMPG Mailbag] Radiator Fan Switch

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Hey, SVOboy, I was wondering if among your list of modifications to the CRX was any thermostatic (or otherwise) switching device to control the on/off function of your electric cooling fan. I'm finally getting around to doing something about that fan running 100% of the time that the car is on; it's so unnecessary. Just wondered if you had done anything with that yet. -Brian
Hey Brain -

Thanks for the note. I haven't actually looked into this yet, as I don't have a problem with my radiator fan running all the time. Is your engine running hot? If so it might not be advisable to switch off your radiator fan lest the engine overheat.

Has anyone else here on EM attempted this or something like it? I know I've heard about it now and then, but I don't recall anyone doing it for sure.

Thanks all, hopefully we can get brian some ideas,
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Old 02-16-2008, 08:12 AM   #2 (permalink)
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http://www.jcwhitney.com/autoparts/P...atalogId=10101

Aftermarket thermostat switches are inexpensive, and will eliminate the ecu and faulty wiring from cooling-fan control. But I've only needed them when the fan wouldn't turn *on*. It's odd that Brian's won't turn *off*. I wonder if he has a CEL...
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Old 02-16-2008, 11:49 AM   #3 (permalink)
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I just did this last weekend...

My CRX Fan Switch writeup:

You'll need:
  • Borg-Warner model # for a CRX Si is TFS500
  • 1-1/16" deep socket
  • Shop towels
  • Clean jug or bucket or tray for temporarily storing some coolant
  • A tupperware bowl
  • Pliers

Put the car up on jack stands and drain out the coolant.

At the passenger side bottom of the radiator is a little spout you can open to drain it. Drain it into a clean jug/pan/bucket and you can put it right back in when you are done, just keep it clean and covered while you work so pets are not tempted to drink it, and nothing falls into it. You can drain a gallon, or you can drain it all, the goal is to get as much coolant out of the engine as you can, so if there's some left in the radiator, its fine.

Now Find the Switch

Crawl under the car, bring your safety glasses, socket, and the roll of shop towels serves as a pillow for your head.

Look between the block and the firewall just above the oil filter. The switch is screwed into the block, and it has two wires plugged into it. The wires are covered with a rubber boot. The boot will most likely crumble, dont sweat it, just get it out of the way and unplug those wires.

You dont need to remember which plug is which. They will work either way, since the switch merely connects them when a certain water temp is reached.

Fast Hands = Less Mess

Now you'll want to have a shallow tupperware bowl positioned on your chest where you can catch coolant that comes out when you remove the switch. Get everything ready and within reach, so you can do this:
  • Loosen the old switch to where its just almost completely free
  • Grab the new switch in one hand
  • Take the old switch out and drop it
  • Quickly put the new switch in and screw it down before a bunch of coolant spills out

The idea is to make less mess! BTW, if you decide to change your oil then it will be much easier to get to the switch with the filter removed, but you'll need to cover the oil filter hole with a rubber glove or something so coolant doesnt get inside.

Ok, you might have to use pliers to get the plugs back on, but you're pretty much done at that point. Dont forget to replace the coolant and 'burp' the air out of it.

The fan should only come on when the temp gauge is a little past the halfway point, then go back off when its cooled down. If you are still having problems, you need to look into the temp sending unit, and/or the thermostat water valve.

Good Luck!
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Old 02-16-2008, 01:36 PM   #4 (permalink)
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Fan LED on the dash

Switches were available at various temp settings in the size I needed. Probably also true for your car. However I'd go with the oem value as they already did all the experimenting to find out which temp to kick the fan on at. As hondaworkshop suggested, if it's not switching on/off appropriately you might need a new switch.

FWIW -
My first FE mod was to remove the radiator's old mechanical clutch fan and put in an electric one.

Part of the project was to install a LED in the dash that shows when the fan is running. Unless yours is a lot louder than I think, you can't hear it when driving, and can barely hear it with the engine off. Thus the LED. With the LED working for you, you can easily decide if you like the way the auto-switching is doing its job.

I got a green LED already set up for 15V (or 12V??) from Radio Shack for just a few dollars. Other colors were available. If you're an electrical nerd you can probably do it for less than I paid.
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Old 02-16-2008, 01:42 PM   #5 (permalink)
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Quote:
Originally Posted by brucepick View Post
Part of the project was to install a LED in the dash that shows when the fan is running. Unless yours is a lot louder than I think, you can't hear it when driving, and can barely hear it with the engine off. Thus the LED. With the LED working for you, you can easily decide if you like the way the auto-switching is doing its job.

I got a green LED already set up for 15V (or 12V??) from Radio Shack for just a few dollars. Other colors were available. If you're an electrical nerd you can probably do it for less than I paid.
When your driving on the freeway and the fans free spinning,
doesn't that cause the led to light up a little?
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Old 02-16-2008, 08:36 PM   #6 (permalink)
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Quote:
Originally Posted by Chris D. View Post
When your driving on the freeway and the fans free spinning,
doesn't that cause the led to light up a little?
Good question, but no it doesn't.
As important as the rad fan is, I'm very glad to know when it's running.

In my design the LED is driven off the fan relay's trip circuit, so the LED never sees any voltage generated by a wind-driven fan. OTOH, if the fan power side of the circuit ever fails, the LED won't tell me.

If you run a bulb or LED off the fan's power circuit it might well light up if the fan spins due to air flow through the grill. I never tried it.

If you're an electrical noob and lost as far as relays, here are the basics:
A basic relay has four terminals. One pair controls the switch within the relay and the other pair receives and sends out power to the fan, through that internal switch. The first pair powers a coil/magnet which operates a switch. When the relay's coil gets power it closes the switch to allow power to the fan. One of the leads to two coil terminals has a temperature switch so the coil only gets current when the temperature switch permits.

Long story short, the two circuits are entirely separate and will have no interference. You can run a light or LED off either one. I decided to not tamper with the very thick and well sealed power leads and connectors to the fan, and instead just tap into the wiring to the temp switch. The last thing I want is corrosion in the fan's power leads.

I added a second switch to the trip circuit so the fan runs on low speed when I use the brake. This provides a moderate air flow when the car is still, mimicking the behavior of a clutch fan. If it ever truly gets hot the temp switch kicks in and the fan then runs on high speed.
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Old 02-16-2008, 09:38 PM   #7 (permalink)
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Nice mods, Bruce.

My fan's run by the ecu. I forgot about the temperature switches; that would be a great reason for it to run constantly.
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Old 02-20-2008, 12:05 PM   #8 (permalink)
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CRX constant-running engine fan

Thanks for the ideas, guys, but I think I'll first try to find out if this fan was intended to run constantly. This CRX HF is an '89. My '91 HF did not do this (to the best of my recollection). Also, this is actually my 2nd '89 CRX HF...and both have had this engine fan run 100% of the time (from the point of turning the ignition switch to the 'accessory' position, the fan comes on...once the car is started the fan remains on until the car is off (i.e., until the key is turned all the way back to the 'off' position).

Guess I'll have to get out the schematics. In the meantime, PLEASE, anyone with an '88-91 CRX or Civic of the same years chime in here...I'd like to get an idea of how many cars have the engine fan run all the time. I DO, of course, realize that some CRXs have TWO fans; these are the cars with Air Conditioning. One of my CRXs has A/C; the other does not. However, both of these CRXs have that very same fan staying "ON" as described in the first paragraph. Any & all help would be appreciated. If this is a problem, then my fixing it will prevent me from having to "mod" a switching component to have the fan only run when necessary. Thanx!!
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Old 02-20-2008, 01:06 PM   #9 (permalink)
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I have a '91 CRX.

The fan should not stay on all the time. The mechanical temperature switch (that I described above) going out is the most probable cause for what is happening. The fan should only come on when it gets a little past halfway ont the temp gauge, then shut off once if falls below halfway. In a way, its good luck for it to fail in the always-on way, as opposed to failing in the never-on way.

If that switch hasn't been replaced as far as you know, then its well overdue. Try it first, and feel free to contact me if you need more details or get in a tight spot. Good Luck!

PS: Fixing it might reveal other problems, once the rest of the cooling system starts behaving properly without the constant help from the fan... but we'll get to that when or if it happens.
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Old 04-12-2011, 04:10 PM   #10 (permalink)
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Quote:
Originally Posted by brucepick View Post
In my design the LED is driven off the fan relay's trip circuit, so the LED never sees any voltage generated by a wind-driven fan. OTOH, if the fan power side of the circuit ever fails, the LED won't tell me.

If you run a bulb or LED off the fan's power circuit it might well light up if the fan spins due to air flow through the grill. I never tried it.

If you're an electrical noob and lost as far as relays, here are the basics:
I recently installed an LED indicator in my 94 civic VX, I plugged the led directly into the fan relay in my fuse box. But I am definitely getting wind powered "light up". Even when the engine is cold. I tried plugging into the other prongs of the relay and the other 3 have constant power when the ignition is on? So please help! Any suggestions?

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