My kid has an 06 civic EX.
it won't warm up at idle. Gauge won't move.
After I drive it for awhile, the gauge climbs to just below half.
Heater blows warm.
read thermostat was stuck open. So I replaced.
Same issue.
Ran for 30 minutes in my heated garage, won't go past half on temp gauge. Blows warm.
upper rad hose gets warm, lower is cold and the rad fan won't kick on?

Thanks

 

Where do you expect the gauge to sit?