Oil pressure slow to rise

[barrett5991]

Hello everyone,

I just wanted to post this as it may potentially be the information someone is looking for in the future.

Backstory, the previous owner of my C85 powered aircraft dealt regularly with oil pressure issues on startup. More specifically, they struggled to get oil pressure to come up within the allotted 30 seconds during startup. This lead to an engine teardown where the oil pump was replaced as well as all of the gears in the accessory housing and everything else that could possible deal with oil pressure (minus the gauge and plumbing).

After having purchased the plane, I did notice that oil pressure was slow to rise on startup. This was in the late spring Florida sun where temperatures were in the range of 85 degree’s Fahrenheit. After moving the aircraft to Utah, fall and winter approached and I began to notice that oil pressure took even longer to rise after startup. Seriously, it got to the point where it would take 59 seconds to come up! Being an A&P, I always like to start with the smallest/easiest possible solution first. That solution was to remove the oil pressure lines and clean them out. Upon removing them, I noticed there was absolutely no fluid in them. Most of our oil pressure gauges work similar to a bourdon tube where non compressible fluid pushes on the gauge to give a pressure readout. If the lines are filled with air alone, the pressure gauge will not give you a readout until the air within the tube is pressurized which takes approximately 40 seconds in my case. This information is not common to most mechanics, including myself, who work on more modern aircraft that do not implement this type of technology. It likely wasn’t common knowledge to the mechanic who did an engine tear down on this aircraft when all it needed was fluid in the lines. I hope this information may eventually help someone who’s faced with a similar problem. Until then, blue skies!

[6298]

It is all well said! I disconnect the pressure line from the gauge and let it drip into a cup until I get a steady flow. Hook it back to the gauge and it’s good to go. Some people put a thinner fluid in the line, but I haven’t seen that to be any better.