Seen different opinions on this, some think it works, some think its totally bogus.
One thing to keep in mind, the motor is designed to operate @ 195°F and as such, you'll get the best wear operating the motor at that temp. Operating at a lower temp can accellerate the wear on the engine, lead to forming deposits on valves and in the crank case, etc.
Running Cooler doesn't give you any extra power, in fact, and it varies amoungst engines, but sometimes running hotter gives more power. Perhaps someone can prove the running the HEMI cooler makes more power, until I see the proof, I'd stay away from this, most of the time it does nothing for power and can create all sorts of problems for you motor over the long term.
The idea is to try to trick the computer into doing some more aggressive tuning because of the lower temperature. I'm NOT convinced that it works in most cases, but its possible. Really depends on the ignition maps based off engine temp, if there is even a variable in the map for engine temp other "at temp X, go to this map". Usually the PCM enters into Closed Loop mode before it reaches operating temp, doubt droping engine temp by 15° would keep you in open loop mode, as if that would give better performance to begin with, and if it did, it would be at quite a cost to the motor in fuel economy and longevity.
If you're going to use a programmer are "Chip", that will have different mappings, then there is NO reason to use a lower thermostat (unless the instructions for the programmer or chip called for it), you're using new maps, no need to trick the computer into sliding to a different part of its old maps.
I'd try to measure the performance, and if you can't find a difference, then put the regular thermostat back, its NOT worth the possible additional problems from running the motor cooler than spec, IMO, definitely NOT worth it if there is NO noticeable performance gain.
Adjusting fan? Do any of the programmers allow you to make changes like that?? You can adjust when the fan turns on and off, or the speed. Chrysler usually has the PCM controlls the fan speed by Pulse Width Modulation (PWM), basically sends electric power to the fan with a square wave signal, varying how wide the square wave of power is, i.e. turning full voltage on for a few millisec, then off a few millisec, then on again. It much more efficient that way. Like I've said before, I'm pretty knowledge on vehicles in general, BUT still a newb on Commanders, NOT sure the Commander controls its fan that way, BUT, most likely it is like most of the other Chrysler vehicles. If the programmer's don't let you make those changes, you have to live with whats in the PCM or make your own circuits to control the fan. PWM is far more flexible and efficient way to vary the RPM and flow of the fan.
Last edited by Mongo; 11-02-2010 at 07:28 AM.