Oil Pressure Head Scratcher

[Greg Ellis]

I have a 63 C model.  I had a funny thing happen.  Not haha funny but curious funny.  I went to Oshkosh this year.  Put a little over 15 hours on the plane to and from.  The first leg was about 3.5 hours.  When I was about 2-3 minutes out from landing, the oil pressure dropped to 59 then down to 57 and fluctuated between the two.  I landed with no issues.  I sat in the FBO for quite a while waiting to see how much oil I had in the airplane and to see if there were any issues.  After waiting, the oil level was almost at 6 quarts but I knew that there was more in there because I only waited about 15 minutes before checking and the engine was still hot.  The oil temp never went out of the green and the highest it got was around 190-195 on climb out and stayed anywhere from 179-185 throughout the flight.

I put in an extra quart at my first stop just to be sure.  I then flew another 2.5 hour leg and landed.  Plane cooled off overnight and there was around 7 qts registered on the oil stick.

So, my question is….Is there anything that can cause a fluke oil reading low in the red even though there is at least 6 qts in the plane?  Anything I should be looking for, maybe a sign of something bad happening?

Cylinder head temps were all good.  Don’t think they ever went above 400 and stayed in the 360’s or so.  I have not had a chance to send my JPI readings to Savvy yet but will probably do that on Monday.

[ShuRugal]

Pull the suction screen and check it for debris. That much of a drop without a change in engine RPM suggests either a leak or a loss of oil pickup.

Sent from my Pixel 5a using Tapatalk

[Greg Ellis]

Just now, ShuRugal said:

Pull the suction screen and check it for debris. That much of a drop without a change in engine RPM suggests either a leak or a loss of oil pickup.

Sent from my Pixel 5a using Tapatalk
 

Thanks.  I will do that next weekend.

[KSMooniac]

I had similar behavior years ago when my level got too low on a long flight. Slow decreasing pressure towards the end, but after adding oil all was good.

Since that is not your issue, I concur with checking the screen to see if there is any debris that might be blocking the oil pickup.

Sent from my LM-V600 using Tapatalk

[Ragsf15e]

Was the power (rpm) pulled back during the event (ie during descent)?

[N201MKTurbo]

If it went down and then came back up, it probably isn’t anything leaking. If it went down a few PSI and then stayed there, I would be concerned. I once had an engine where the oil pressure dropped a few PSI and just behaved a little different than usual. It turned out to be a gear shaft coming loose. It was a few hours from a complete engine failure. Yours could have been due to a piece of crud getting stuck in your pressure regulator.

[Greg Ellis]

2 hours ago, Ragsf15e said:

Was the power (rpm) pulled back during the event (ie during descent)?

Not at the time that it happened.

[Greg Ellis]

5 hours ago, M20Doc said:

How much of a drop was there?  Electric gauge, or old mechanical gauge?  I would test the oil pressure with known test gauge first.
 

 

The oil pressure was on the EDM 900.  It usually runs in the green anywhere from 64 - 67 in cruise.  It dropped to the red which starts at 59 went down to 57 and fluctuated between the two.  And as I mentioned in the original post, this happened on the first leg which was about 3.5 hours of 15 hours of flight time and it did not happen again.

[Greg Ellis]

3 hours ago, M20Doc said:

From the Lycoming 360 series operators manual, your oil pressure is already at the lower end of the range.  I’d pull and clean the relief valve, then adjust the oil pressure toward the higher end of the range and confirm with a known test gauge.

Just looked at page 2 of the AFM for my airplane.  This is what JPI used when they adjusted the settings for my EDM 900.  It states low pressure is 60, high pressure is 85 and of course green arc is from 60 - 85.  So I am operating in the green arc but at the lower end so I will have all of what you mentioned checked out.  Thanks.

[M20F]

15 hours ago, M20Doc said:

How much of a drop was there?  Electric gauge, or old mechanical gauge?  I would test the oil pressure with known test gauge first.
 

 

This, people love to fire the $$ cannon in aviation.  Start small and cheap then work your way up. 

[KSMooniac]

I concur with M20Doc re: setting your oil pressure.  Lycomings benefit from higher pressure since that is the only way oil gets delivered to the heads/rocker arms (except for the Bravo engines).  I cranked mine up after overhaul so that I run in the mid- to upper-80's in my J (green arc to 90).  The re-start Cessnas have a green arc to 110 or 115 psi with essentially the same engine!  Funny Textron/Lyc never explained why they did that.  Hopefully your situation is nothing more than a bit of debris blocking the pressure relief valve and not big debris in the sump blocking the pickup.

[cliffy]

Check and reset the electrical connections to your engine gages

Slightly loose connections can cause issues with electronic gages

If you have spade connectors in the lines pull them apart and reset them also

You might have slight corrosion on the contact surfaces

Like said above Do the cheap and easy fixes first rather than throwing $$$$ at the problem

[M20F]

15 hours ago, cliffy said:

Check and reset the electrical connections to your engine gages

Slightly loose connections can cause issues with electronic gages

If you have spade connectors in the lines pull them apart and reset them also

You might have slight corrosion on the contact surfaces

Like said above Do the cheap and easy fixes first rather than throwing $$$$ at the problem

Dremel tool them with a wire brush and then dylectic grease everywhere for the win. 

[N201MKTurbo]

FWIW, the oil suction screen is the oil pickup. If you search for my engine overhaul pictures you will see that in the sump pics.