When the engine is cold (at first start up) the ECU runs the car in an "open loop" mode, which runs the car rich, causing it to heat up to operating temp quicker.
So by installing a low temp t-stat in cold weather, it extends the "open loop" mode, causing the car to run richer longer, which eats up gas quicker.
I lost 2-3 mpg running a 170 t-stat when compared to 180 degree t-stat, both in 30-40 degree weather.
So a a 160 t-stat could cause even greater (depending on mods).
