i just replaced my t-stat in my lumina (3.1) and wow what a difference. it always ran cooler than other 3.1's, but after changing the t-stat it bumped up about 20 degrees to where it should be on the guage. right now i have half the radiator covered with cardboard cus it hasn't been above freezing in a few days. that kinda helps it heat up faster. my monte heats up pretty well without anything covering the radiator.

 

yeah, flushed out the system, ran the cleaner, changed the stat, refilled the system, runs great now.. even at -27 the needle sits a lil below half with theat on full