Gauges
The liquid in the gauges is usually glycerine. The purpose is to dampen the needle movement. The liquid can cause errors when the temp is high and they dampen too much. Pressure can build up in the gauge from the heat and cause them to read low. This is because the gauge reads differential pressure and the pressure in the gauge is different than ambient pressure outside the gauge. The error isn't much, less than a few PSIG. If you don't have a problem with the needle bouncing around, I'd just stay with the standard gauges. JMO.