PWM cooling fan(s) control using ECM

[andrewb70]

So........

I am not ashamed to admit that I might be slightly obsessed with the ability to control my fan speed.

Recently I had to add coolant to my system (I was running straight water in the summer) so that I don't hurt anything during the long WI winter. After adding the coolant (good to about -40 degrees) I noticed that the engine ran about 4-5 degrees hotter under previously noted conditions. This of course caused the fan to run faster per the table that I programmed.

So I decided to "retune" the table and just set it to work the best it can in my car. For me, "the best it can" is running the fan as slowly as possible, while maintaining a target temperature. But what is that target temperature? LOL

I know I have a stock thermostat which by all accounts is 187 degrees. Given that information I can turn off the fan and just watch what the temperature does under varying conditions (granted all of this is dependent on ambient temperature and ideal I would incorporate it into the fan control strategy for optimal results, but even GM doesn't do this...Didn't I say that I might be slightly obsessed?)

Driving normally around town (aka like grandma...top speed 35) the temperature never got above 191-192 (about 50 ambient). I then took it on the highway and cruising at a steady 75 mph the temp was stable between 194-195 degrees (all this with the fan off).

So I configured my table as follows at vehicle speed below 40mph...

Temp:fan %

194:5 (off)
200:10
210:20

Then it ramps in rather quickly (I don't recall the exact numbers). The fan basically never kicks on around town and temps is steady at 191-192.

For vehicle speed above 40mph I just configured the cells to be one value off, like this:

194:5
200:5
210:10

etc....again, ramping in quickly. Temp is steady at 194-195 without the fan.

I don't know if this is optimal in terms of thermal efficiency. Probably not because my engine seems to run cooler than it would in the donor vehicle (2009 Colorado pick-up). But in terms of my target goal (cycling the fan as little as possible) I think I succeeded.

Anyway, I thought I would share for anyone that cares.

Comments, questions, and opinions welcome.

Andrew