Cooling fan control

Got a question for you electrical minded folks.

A stock computer sets the fan on at 210 deg F.
Does anyone know what voltage from the temp sensor is at 210deg F?

The end result being, I'd like to know how to install a resistor in order to have my fan come on automatically at like 195 or 200 deg F instead.
Ususally I just drive with the a/c on, which frequently cycles the fan due to the compressor kicking on.
But I'd like to have this all set to happen automatically, without a computer reprogram on my girlfriend's 92 Acclaim TBI.

I figure a strategically selected (and placed, not sure if it would have to be in series or parrallel) resistor would accomplish this. I don't know what the voltage schedule of the sensor is through the operating temp range.

Anyone out there already figured this out?
Thanks
Wayne Hemingway
91 Dodge Spirit ES T1 5spd Intercooled
89 Plymouth Acclaim T1 Auto Intercooled (THE Slugmobile)
92 Plymouth Acclaim TBI

[Mike M]

http://minimopar.knizefamily.net/ecu...t_temp_se.html

There is some info there, whether you can use it or not.

It's very easy to add a switch to control the fan. You can simply run a grounded switch to the trigger wire on the cooling fan relay. This way the computer retains control of the fan, but you can override it.

thanks Mike, I'll check it out.

yeah, if it were for me, I'd just use the same override switch i have on both my Spirit and on Slug.
But, the girlfriend will need this to be a automatic operation.
I'd like to do this to try and extend the life of the car she'll start driving shortly. I'm going to put a 180 T-stat in it, and I want the fan to kick on early so it doesn ever get to 210.

thanks for the info!
Wayne Hemingway
91 Dodge Spirit ES T1 5spd Intercooled
89 Plymouth Acclaim T1 Auto Intercooled (THE Slugmobile)
92 Plymouth Acclaim TBI

the coolant temp sensor at the t-stat is not the same one that reads to the temp gauge, right?

[91DSX]

Quote:

Originally Posted by wheming the coolant temp sensor at the t-stat is not the same one that reads to the temp gauge, right?

You are correct Wayne, with the 180 t-stat and having a 1/16 hold drilled through it she shouldn't have any problems, if your still worried install a 160 degree t-stat.

P.s. It sure is good to know Gus'(R.I.P.) Slugmobile is in good hands

Thanks Roger.
Yeah, its not so much that I worry about the normal operating temp, with that lower t-stat. The real concern is now I'd like to have the fan kick on with that same temperature offset. So with a 180 I'd like the fan to cycle on at 195-200.
if it's not something that can be figured out easy, I might just live with it or have someone just tweak that one thing in the computer. I heard Gary D won't do computers anymore. Is anyone else out there doing them?

And yes, Slug is very much alive but has yet to be true to her heritage. She seems to have had some problems since I starting taking care of her, and those need to get straight before she can make a true racing return. Although, she still was very capable of running a couple high 12's at SDAC-13.
Wayne
(what happened to my sig anyway?)

[charger R/T]

I've read some guys tie a wire in on the ground wire from the computer to the relay and put in a toggle switch so they can turn it on when they want. Instead of the toggle switch locate a temp sender that is an on off type (not variable resistance) and set for 195 and install it in a coolant passage. I have a TIII so I don't have an 8v here to look at but I think I have read there is a plug near the thermostat housing you can use. Most trucks use shut down systems and there senders are on off not variable like the senders used on gauges and they can be had in all temp ranges.

Changing the fan schedule is a good idea. I just had to change the thermostat in my lebaron it was stuck open and even with it open in my garage it would at idle get high enough to turn on the fan at 210. So even with no thermostat it still runs at the computer setting not the thermostat setting.

You don't want to cut the wire from the computer because you still want it to turn on with the A/C.
If you need more info PM me or post here.
Tim

[DarkWolf]

I just run an aftermarket fan controller that I picked up from advanced or autozone can't remember for $20. Its basically a relay with a probe that you stick in the upper radiator hose and it has a nob on the top that you use to adjust the temp it kicks the fan on at.

Yeah, that's true.
I can just use an aftermarket adjustable to switch the same ground wire on the fan relay (I think its the purple one?) instead of a toggle.
I'm fine with the manual toggle on my stuff, it works great. Just needs to be an automatic operation for the girlfriend.
I can't even get her to understand why you allow the car to warm up before getting in and jumping on the gas...

Thanks for the good suggestions!
Wayne

[Frank]

Usually thermal resistors run in the range of 300 to 400 ohms. Measure yours once it warms up. You can do this by disconnecting it, using an ohm meter to check the resistance from the main terminal stud to ground.

You will want to make it pretend that it is running hotter then it really is. This means you need to reduce the resistance of the temperature sensor (thermistor - variable resistor that is effect by temperature. uses a non linear curve that is inversly proportional to the temperature).

So what is a good way to reduce the resistance? A resistor in a parrallel circuit is the easiest. You would connect this resistor from the temperature sensor wire, to ground. Since it is in parellel, it needs to be of very high resistance to drop the overal resistance read by the computer just a little in hopes to estimate a good temperature drop.

The equation for parallel resistance is as follows:

Rt^-1 = R1^-1 + R2^-1 + R3^-1 + ..... + Rn^-1

Rt = Total Resistance
R1, R2, R3, Rn = are the resistors in parrellel. As you can see, you can have as many as you want.

Lets assume that you measure R1=350ohms, and you want to reduce the resistance by 20ohms to achieve Rt=330ohms.

330^-1 = 350^-1 + x^-1
x = 5775 ohms.

Since the nearest common resistor is 5800 ohms, you would need a Green, Gray, Red resistor. If you let me know what the resistance when it warms up, and just before it warms up, I can get you all the information needed to ensure proper tempature control.



Frank

[looneytuner]

It won't work. When a hose blows and steam comes out, and the engine starts rattling, she will think the muffler is falling off and drive it home for you to fix. Then you will be even more STEAMED at her after all the work you did.

"Incompetence is a state of mind caused by too many years on computers".

[contraption22]

I use a fan controller from Painless wiring... threads into the tstat housing, turns the fan on at 185, and off at 170.

Thanks Frank and Mike.
I'll have to look into getting some measures of the resistance. Maybe I can look into it next week on my days off.
I have a fan controller I use on my Nova that I put on an electric supplemental fan. I could always buy another of those. I think its a Perma Cool. Came from JEG'S, anyway.
Although I do like the simple add a resistor idea, as I first intended.

Thanks for the info!
Wayne

[Frank]

No problem. E-mail me anytime, I dont mind. I can get that faster then checking TD for updates or questions.


Frank