The line, bulb, and gauge are filled with some sort of liquid. If any part of the gauge assembly leaks, or gets damaged, the whole thing is shot and will need replaced. The good news is, most of the vender's sell and repair gauges. You can buy a cheap-o aftermarket gauge and use the same fittings in the block for a quick test. As for getting air out of the system. Drill a 1/8" air hole in the flange of the thermostat or place a aspirin in the thermostat as you hold it open with your fingers. Once coolant fills the system the pill will dissolve away. You will never get the t-stat to open with out coolant touching it, hot air or even steam will not do it.
Joe
