Air in the oil sender line...

gasman · #1 07-02-2019, 10:33 AM

It comes up now and then to purge air out of the oil sender line. When I installed my senders on the top corner of the motor mount by the firewall, I did not purge the air out of the line. The Van's gauge has worked flawlessly. Later when I added a second sender to the MGL, there was no oil in the existing fitting and no mess.

My point is, pressure is pressure. It doesn't matter if it is water, air, oil, propane in a liquid or gas state. Your oil pressure will compress the trapped air to the point of the pressure value placed on the oil, no more, no less. In fact, the trapped air gives a cushion to the gauge which may prolong it's service life.

Larry DeCamp · #2 07-02-2019, 10:54 AM

As proposed above, my oil pressure is very consistent, independent of atmospheric pressure. However, my fuel pressure is strange. With carb engine and boost pump, the indicated pressure seems to vary with temperature. The engine pump may only show 1+ psi and the boost pump will raise it a couple. In colder weather the pressure is generally higher. It also changes with significant altitude change, presumably due to temp change. With Vans xducer and gauge, what is the problem and possible correction ?

gasman · #3 07-02-2019, 08:15 PM

My O320 E2D produces 3+ lbs and adds about 1# more with the boost pump.

Have you ever tested it with a mechanical gauge?

Larry DeCamp · #4 07-03-2019, 06:36 AM

Gasman,No I have not confirmed with mechanical gauge.
If transducers use an ambient pressure reference, then indicated pressure would increase with altitude . If this is valid logic, the pressure reading from a transducer ( fuel or oil ) would also very from any barometric pressure variance. If someone can set me straight on how transducers work, I will make some accurate observations regarding my mystery fuel pressure characteristics.