manualing the electric fan

I've installed a tranny cooler in front of the radiator directly in front of the electric fan, will I hurt anything by unplugging the thermostat sensor to make it run constantly while on the trail? The CEL comes on, but goes away when the ignition is cycled.

1993; 4.0; auto; no A/C

Why not just run a override switch?

If you do that, it will be off when it needs to be on, and depend on you remembering to switch it on every time.

What about putting a small dedicated fan on the transmission cooler?

Weaselton said:

I've installed a tranny cooler in front of the radiator directly in front of the electric fan, will I hurt anything by unplugging the thermostat sensor to make it run constantly while on the trail? The CEL comes on, but goes away when the ignition is cycled.

1993; 4.0; auto; no A/C

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Your 'thermostat sensor' is so the computer can monitor the engine temperature, so that it can set the air-fuel mixture, control the timing, etc. You need to keep it plugged in or the car will run like a dog.

It's pretty easy to wire up a switch, search

Quick thought: If you want the fan to default to stock operation when you're drving, get a relay, wire it to bypass the fan switch, actuate it with the 4WD light switch, and fan will come on whenever you shift into 4WD. If you live in an area where it snows a lot, you'll also need another switch to deactivate the relay in winter.

Option two, not simple unless you have some access to parts: use a latching relay that actuates with a momentary contact switch. Put a button on the dash (or use a rear defrost switch). Push switch to activate relay, which now stays on until you power off. It will always default to normal operation. I haven't checked the availability of 12 volt latching relays, but I expect they're out there somewhere. For those unfamiliar with this, a latching relay has an extra set of contacts which, when on, duplicates the circuit used to activate it. Once it's on, it stays on until power is removed.

If you can't find a 12 volt latching relay for fairly cheap, it's not hard to wire one up. Get a second relay (or a DPST relay), wire the coils in parallel (85 to 85, 86 to 86.) Wire the switch terminals on one relay (or one half of the DPST relay) to whatever you want to switch. Wire one side of the switch (87 or 30) on the other relay to +12 volts and the other (30 or 87) to 86 on either relay. Wire 85 on either relay to ground. Run a wire from your switch (which should provide 12 volts when you want to turn the fans on) to the anode (non stripe end) of a diode, then the cathode (stripe end of diode) to 86 on either relay. The relays will stay off till you press the switch which energizes the coils on both, the second relay now will continue to provide 12 volts even after the switch isn't pressed anymore.

If this is too confusing I can mspaint a diagram for you.

Johnnie Walker said:

Why not just run a override switch?

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I am wondering the same thing. the timer and all this wiring looks great. But i had this same problem with my 00 when on the trail we fixed the problem by pulling the relay and making a jumper to have the fan run all the time. Of course you have to watch how long you let the fan run after you shut off the ignition. So while we were standing around talking about it an electrian that was with us said why not just run that jumper wire with a switch in it and then put your relay back so it works normally? this will allow you to turn the fan on whenever you want to you, just have to make sure the switch is turned off if you have the heep off and are going to walk away form it from any period of timeas it will drain our battery pretty fast...

Why is everyone ignoring the simple solution, a dedicated small fan for the transmission cooler?

winkosmosis said:

Why is everyone ignoring the simple solution, a dedicated small fan for the transmission cooler?

Click to expand...

The e-fan was there for the A/C condensor anyway i thought? I have no A/C so.....why not use it.
Ok I will run power directly to the fan then from a relay. Will it mess up if i am running it while wheeling and the normal system tries to kick it on?, like overload it?

The fan already has a relay that is activated by the computer closing a ground wire whenever the sensor indicates high temperature or A/C compressor clutch engaged. Easiest thing to do is splice into that wire with your own ground signal using a switch on a piece of wire that's grounded to the body, then you can just toggle ground to the relay as needed (you can even add a third pole that sends the signal nowhere to make a fan kill switch). Some people get a check-engine-light when the ECM sees your ground bleeding back on the wire, but it shouldn't be a problem for your setup. If it is, just put a diode on the wire that goes back to the computer so that the ground signal can't travel backwards down that wire.

Thanks, E-hall, thats the info i was looking for.