Dash temperature gauge / coolant temp sending sensor

[SA_trucker]

Well, some how I got it sorted out and I'm back in action. Over the weekend I drained enough coolant to remove the temp sending unit - wire brushed a little bit around the housing there. I also replaced the thermostat (because I bought a new one and just figured since the truck has 294,000 miles, why not). Put it back together and refilled/burped the coolant system and - magic - temp is reading again on the dash.

I don't know what the exact issue was, but its working again and I'm happy. Thanks everyone for helping me think through it!