[blazee]

Okay here we go:

The thermostat doesn't fool the computer, the thermostat lowers the engine operating temperature.

When an engine starts up, it runs in "open loop". While in open loop the computer uses default settings to operate the engine. After the engine warms up to a set temperature, it switches to closed loop. While in closed loop the computer actively controls all aspects of the engine to provide optimal performance.

If you use a lower temp thermostat in conjunction with a programmer there is no problem because the programmer will set the PCM to go into closed loop at a lower temp. The engine will operate more efficiently at lower temps, because it will have a denser air/fuel mixture. (molecules contract when cool and expand when heated) With the denser mix, the engine gets more energy per volume in the cylinder.

You should never use a lower thermostat without reprogrammimg the PCM, because the computer will never go into closed loop. This will make your fuel economy and performance suffer.