Quote Originally Posted by Donkado View Post
Before I replaced the thermostat the old one when running wide open would hold at 160. Is there a way to test the gauge?
What is the gauge reading completely cold with the key turned on, but not running? Does the 05 have closed loop cooling or sucking lake water (impeller, so I assume closed loop)

Analog gauges with bad grounds and/or lose connections will never read accurately. I would check the back of the dash for any lose connections. Next think about your water pump (not impeller) on the engine. If it is starting to fail it could not be pumping enough to cycle the antifreeze through. Most have weep holes that drip coolant when they are about done working (on cars anyway).