I now have the luxury of setting the fan turn temp to whatever I want, since I can burn my own chips. The factory setting was about 226degF ON, 220degF OFF. I lowered it to about 185 on, 179 off. But this controls only the primary fan. I was wondering if I could run a jumper over from the output of the ECM, green wire, which turns on the relay, to secondary fan relay. That way the ECM would turn on/off both fans when I want it to. What I am asking is can the ECM fan control output drive 2 relay coils, instead of one?

On the other hand, I have a Hayden thermal switch installed in the radiator. It is supposed to close at 185, open at 170. I have this wired thru toggle switches to each fan relay. From my scan tool, I noticed that the Hayden actually closes about 200, and opens at 181, at least that is what the ECM sees. I guess where the Hayden switch is mounted, and where the coolant temp sensor is, are 2 entirely different temps.!!

If I set the primary fan turn on temp lower than the Hayden, the secondary fan may never come on, unless it is really hot out and the one fan cannot cool the motor. I may just tweak the primary fan turn on temps with the chip, and just let the Hayden switch control the secondary fan.

Thanks for any input.

------------------
Best ET 14.413 @95.57 without
pulling valve covers or manifolds.
Also with stock 2.77 rear end!!!

 

Mike,

Personally, I'd set the primary fan to about 185°-175°, and keep the hard wired secondary fan sensor to operate the secondary relay and fan as a failsafe. If the CTS for the ECM ever goes belly-up, you could be toasting the engine without the backup. I doubt that the secondary fan will ever operate if the CTS remains operational though. One fan should be enough for most conditions, and two fans may be an unnecessarily heavy electrical load on the system, especially at idle. I would suspect the ECM pull-downs would possibly operate two relays without overheating the transistor, but I'm not sure. It's your ECM, and you can try it if you want, but I'd be cautious.

------------------
Later,
Vader
------------------
"What a Day..."
Adobe Acrobat Reader

 

Thanks for the reply, Vader. I allways like to hear someone elses comment on an idea that I have. BEFORE I could program my own chips, I had the Hayden switch turning on both fans at the same time, to cool the motor. Like I said, I think it oscilated between 200 and 181, but I had no control over those trip points. I was wondering if that puts extra load on the motor, esp at idle. And it probably doesn't help when I run down the 1/4, since I just flip the toggles to ON when I run.

If you consider what GM did with our cars that had dual fans, they didn't turn both on at the same time, and the secondary fan, called "heavy duty", was only used when the switch saw about 238F. Or when the A/C was turned on.

I think I will just control the primary fan with the ECM, playing with the fan turn-on temps. I will pay attention to how 1 fan cools the motor by itself. I will use the Hayden just to control the secondary fan. That way if the primary cannot cool the motor, or it starts to heat up at a redlite in the 80's, the second fan will kick it, and I know that won't let it get over 200F.
This way the circuits that I added will be seperate, and I won't have any crosstalk between the 2 fan control circuits.

Thanks for the advice on running 2 fans off the ECM. It probably isn't needed. The temps where I live only get up to the high 80's, and I don't have to drive in heavy traffic hardly at all.