How does a factory water temp sending unit work? Does it ground when it reaches a certain temp? I was looking at a couple of intake manifolds I have today and got to thinking that the sending unit might be a good cheap way to turn on my electric fan. I have two different ones, one for a temp gauge and one for a idiot light. I was thinking, hook the ground from the fan to it, and when the water gets hot, it will ground and kick in the fan. Or will the temp be too high before the unit grounds and turn the fan on too late?
The sensor in my Ranger's fan circuit (Painles wiring kit) does nothing but function as the signal for the relay switch. So in effect it doesn't actually turn the fans on. Some temp sensors use grounding to function, some don't (I think) If anything, you'll need to wire in a relay switch along with the temp sensor.
Temperature sensors for idiot lights are nothing more than a switch. They are designed to switch at a certain temp. You could not use one to switch on your fan because it switches at a much higher temperature than you would want. Thats why you have to use one specifically set up for fan operation. Sensors switch the ground side of the relay. They pick up the ground through the base. A relay does not care which side is used to turn it on or off.
For $25.88 @ Summit, this one is a good alternative. It's adjustable from 160°F to 240°F, but you'll need to wire a not included relay. pn.FLX-31147
I used a kit similar to that on my Ranger before switching to the Painless kit. The reason I swithced was I couldn't rely on that kit to function properly, the temp at which the fans came on was never the same. Then they wouldn't turn off. It didn't use a relay either.
Thanks Dennis for confirming what I thought was true. I was hoping to stay away from the ugly kits like that one 1slow7t, was really just wanting to hook a single wire to a sensor on the block, and not having to use a thermocouple like that hooked to the hose. I'll check the painless kit, baddad457,and see if it looks any better. I may just wire it hot all the time, because if I put it on a manual switch, I'll forget to turn it on, and end up frying the engine!
...put the ..manual switch...on and then wire the...factory water temp sending unit...to your horn...that will come on if you forget, to remind you to turn the fan on... ...BFF...
The painless kit has a single 18 ro 20 ga wire going to the sender. Really easy to hide. Mine comes in from the firewall and runs along the underside of the Holley carb's fuel line using tiny black tie wraps, to the sensor, that can be T'eed off on the intake with the heater hose nipple, or not depending on your intake & the number of coolant ports. You can hide the relay switch somewhere else. I wired a manual switch into the system as insurance, but it's never been used as such, the kit has performed flawlessly for years now.
Regardless of how you turn it on and off, the fan definitely needs to be on a relay. Electric fans pull alot of power. My fan is just on a manual switch on a relay. I usually just leave it on all the time when driving around town. Whenever I get on the interstate, or know I'll be moving at a decent rate of speed for an extended period of time, I turn it off. To me turning it on and off is just second nature now, I pretty much just do it without thinking about it. When I'm driving other cars, I've found myself inadvertently hunting for the fan switch several times. I don't see why you couldn't just get a sending unit that turns on at around 180 or 190 and wire the ground wire of the relay to that. I would look into older cars that had electric fans like old Honda's and stuff and see what kind of temp sending unit they have. I'll bet they work similar to that. As for the relay, you can wire a switch on the ground side or positive side of the relay, dosen't matter as long as the opposite has either constant ground or constant power.
mine is ...switched on power...through a relay. this way i can hear the fan before i start the car... that way i know it was working when i left... i have a 2 speed fan...H/summer...L/winter... i was thinking about wiring the H/side to the ...A/C compressor wire... i wonder if there would be a problem if the L/H sides have power at the same time ? ......
