2001 Impala Temp Gauge Problem

My '01 Impala has a strange problem. The temp gauge all of a sudden went to below 140 and won't rise at all. The coolant levels are good, but tha upper hose to the radiator gets hot after 20 minutes (normal hot), however the lower hose to the water pump stays cool. And here's the really weird thing, i can open up the radiator cap and the coolant is not hot. Any Ideas? Also the car has good power, engine sounds and runs good.

Question: What size engine? did you see water flowing when you had the cap off? Possible stuck open thermostat...but should still see coolant flowing if left running long enough...how many miles on this?

I had a similar problem... My temp gage would not move off the bottom... My thermostat was stuck open and for some reason the radiator fans were running constantly, probably due to the error code being generated... I ended up replacing the thermostat, coolant temp sensor and I had to clear the DTC code a couple of times before things went back to normal... I have a 2001 LS with he 3.8L motor...