Low Oil Pressure

miyu1975 · #1 10-09-2012, 07:31 AM

I have been seeing lower than I'd like oil pressure lately. I have the Kavlico transducers hooked into the Skyview, (just changed from the dynon transducer). I also recently added 2 washers in the oil relief valve. After adding the 2 washers I noticed the oil pressure at idle went from 60 to 71. Ok so far. I haven't flown in a few weeks, due to my airport being closed for runway improvements, so yesterday I finally got a good hour flight in. I noticed again at idle OP was low 70s, at cruise (23MP 2500rpm, 200 oil temp, showing 170TAS) I had 51 oil pressure. I knew this was on the low end, actually the book says 55 min. Had 5 qts mineral oil at takeoff.

Also, prior to adding the 2 washers I had low 60s OP at similar power settings. That was also with the standard dynon OP transducer, which I have now switched to kavlico. So yesterdays flight was the first time with the 2 washers added and the new kavilco transducer.

So, I have been searching the forums and have a few places to start..

1. Check the electrical connectors on the ground wire on the tranducers

2. bleed the transducer lines....How do I do that?

3. I could add another washer to the relief valve. ??

4. Add a qt oil and takeoff with 6 qts, and see I have a change in OP with more oil

....what else if any...hopefully #1 will have good results.

airguy · #2 10-09-2012, 07:34 AM

Put an analog gauge on it to check your sensor.

miyu1975 · #3 10-09-2012, 07:36 AM

Now that I think about it, I changed the oil and fuel transducers at the same time and connected those 2 ground wires into one ground wire off the SV ems. I probably should have ran them separate. I will certainly start there. Clip the ground wires and run individual grounds directly back to the ground bus..

DEWATSON · #4 10-09-2012, 08:22 AM

Will someone explain to me why it is necessary to bleed the air from oil pressure lines to get an accurate oil pressure reading? I don't understand why this will change the oil pressure reading at the gauge. Thanks.

miyu1975 · #5 10-09-2012, 08:25 AM

me either..I just read it on other threads of the same topic

DanBaier · #6 10-09-2012, 08:39 AM

The simplest first step is probably to add 1 quart and see if there's a change. (I've seen Lyc's start to drop pressure around 5 quarts.) If nothing seems different, then the next step would seem to be checking the gauge.

I wish I could recall where I snatched this image from, but it does illustrate that there are different readings depending on where you pick up the pressure.

Dan

DEWATSON · #7 10-09-2012, 11:29 AM

The oil pressure shouldn't be different no matter how much oil is in the engine if the pump never cavitates or loses prime. I don't understand why the oil pressure should increase by adding a quart of oil as long as oil stays above the oil pump pickup inlet at wide open throttle. I need help understanding this.

molson309 · #8 10-09-2012, 12:08 PM

Quote:

Originally Posted by DEWATSON

Will someone explain to me why it is necessary to bleed the air from oil pressure lines to get an accurate oil pressure reading? I don't understand why this will change the oil pressure reading at the gauge. Thanks.

It doesn't make any difference if there's air in the line or not as long as there is not a leak. What air in the line can do, though, is dampen pulsations you might otherwise see.

After a certain number of hours the air usually works itself out anyway; I replaced a fuel pressure sensor a year or so ago and the line, despite never being bled, was full of fuel.

jrs14855 · #9 10-09-2012, 12:15 PM

Most of the four cyl Lycomings have a minimum oil level betweeen 2 and 3 quarts. The oil pressure absolutely should not be affected by any oil level between minimum and full.
Oil pressure in cruise should be middle of the green. Oil pressure below the green, if this is really what is happening and not a instrument issue, is a good way to destroy a Lycoming.

DEWATSON · #10 10-09-2012, 12:44 PM

Thanks for both answers. I agree, but I read things on this forum every now and then that oppose the laws of physics. I was just curious to know if there was something I was missing about airplane engine behavior.

It seems to me that if the air disappears from a fuel or oil pressure line over time, eventually you should see signs of fuel or oil outside of the line somewhere if it is working out from the instrument end.