Re: Mechanical oil pressure gauge
Having air in the line can have advantages and disavantages...
With air in the line, it has a natural dampning effect....hence, your needle will not bounce as much or show the pulses in the oil.
Without air, the oposite is true....the needle will show 'all' pulses. (one of the reasons they make oil filled gauges)
But as you have found, pressure is pressure. But make sure you heed Leve's advice ....protect that line. I have seen a few guys that ended up with a floor board full of oil.