bsacks05

bsacks05

Well Known Member
My O320, 160hp, carbed engine has always indicated an oil pressure of 65psi while running. This morning on downwind and 1500rpm I noticed the pressure in the 40's and on final near idle it dropped to the 20's. I cleared the active and apply near full power with brakes and the pressure came back up to the 60's. I haven't had time to look at it yet.

In the last month I changed the AN fitting from the engine to a steel one because the al. one cracked after 830 hours. (Don't ask why I used an al. fitting there, I don't know myself. That was 8 years ago.) It has flown 8 hours since then with a steady 65psi until today.

Any ideas before I tear into it this weekend?
 
oil pressure

Steam gauge or electrical?? If electric make sure the sender is properly grounded.
The next step would be to remove the oil pressure relief valve housing and clean the ball and seat. if the ball is not perfect, replace it. Next check the oil screen/filter and remove and check the lower screen.
You may also want to do a compression check and oil analysis.
Google Bill Marvel oil pressure, this will take you to a LOT of information on Lycoming oil pressure.
I am a firm believer in high green oil pressure for the Lycomings. I would not even consider flying with 65# in normal cruise.
 
I am not even remotely a expert on the engines but your current readings seem in line with what I would expect to see. The constant 65 psi seems like the aberration in readings. I don't recall flying a plane where oil pressure did not track RPM to some degree and 25 psi is allowed at idle.

George
 
Your readings are perfectly normal. Please don't "tear into" anything.
Perhaps you are mis-remembering. You should not see 65 psi at idle after the engine is warm.
 
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Clean the screen!

Not too many remove the sump screen and clean it every oil change,most engines are returned to Lycoming at and past TBO with the paint still untouched on and around the screen cap.This may not change anything but its an important maintenance item(as per Lycoming).May I ask what oil are you using? Have you added Cam guard?
RHill
 
Mel,
Is there a need for a metered orifice in the fitting off the engine to avoid fluctuations?
Thanks!
 
Actually the orifice is there primarily to minimize oil loss in case of a gauge/sender failure. You should not need it to control fluctuations.
 
I never noticed the pressure fluctuating with rpm before. It does not spike or jump like a bad ground. Normal? Ok. I will still look at the oil pressure control valve for debris. No, I did not mean I was gonna tear down the engine. Just meant to say I was gonna remove the cowl and have a look around. Also, I remove and clean the finger screen every oil change.
 
oil pressure

Mel-
If 65# is ok maybe you can explain why all Lycoming powered Cessnas are running 90# in cruise??
Have you ever read the Deakin/Scott articles??
 
I never noticed the pressure fluctuating with rpm before. It does not spike or jump like a bad ground. Normal?
Click to expand...

If oil pressure relief valve is working correctly, then it does not jump around at that's normal.

I think an earlier poster suggested you take a look at that. Once I was sure of the reading (no issues with gauge, etc.) then that's probably what I'd check next.

Dan
 
jrs14855 said:
Mel-
If 65# is ok maybe you can explain why all Lycoming powered Cessnas are running 90# in cruise??
Have you ever read the Deakin/Scott articles??
Click to expand...

I have no idea why Cessnas operate at 90 psi, nor do I know where they take their readings from.
I do know that the Lycoming manual says that normal oil pressure should be 60-90 psi at operating temperature with 25 psi at idle.
I have read most of Deakin's articles. Not sure about the one you are referring to.
 
oilpressure

I misstated that-should read Bill Scott/Bill Marvel articles. These explain in great detail the high oil pressure settings in then Lycoming powered Cessnas since Cessnas restart of single engine production and the reasoning for this higher setting.
 
PROBLEM SOLVED....but....

I finally pulled the oil pressure regulator and found this inside:

2wbujcx.jpg


2e2fm1j.jpg


It is some sort of gasket or o-ring made of rubber and I could not tell where it came from. It was just in there kinda folded over. I googled and found that Ted Chang had a similiar mystery part after he had a similiar oil pressure experience. His engine is from Aerosport, mine is from PennYann.
I replaced the valve, ran up the engine on the ground and my pressure indicated 65psi as before with very little fluctuation, just as it has been for all of the 835 hours since the engine was built.

What is this mystery part? I will call PY to see if they can tell me anything.

Regarding fluctuating oil pressure being normal with power changes, I guess that is true from what I read but my pressure has always changed very little. Maybe 62-66 psi. The engine run data says that the pressure ranged from 78-82psi. through all power settings including idle but that was when it was new.
 
Bruce,

I did not read this thread until now. Of course we have already communicated through PM. Here I just want to openly share my experience.

I had a low oil pressure problem two years ago. After opening the oil relief valve I found a broken plastic gasket under the ball:
oilpressuregasket.jpg

It jammed the ball and allowed oil to pass through. I went to FBO searching for a replacement and was told that they have never seen anything under the ball. They checked the engine book and showed me that there is no such gasket. I removed it and re-installed the relief valve, the low oil pressure problem went away. It was 440 hrs ago and my oil pressure has been normal (I did have a failed oil pressure sender early this year. It gave me a high oil pressure reading until I replace it. Of course it is not related to this one.)
 
My parts and overhaul manuals + Lycoming library are all out at the hangar, so I can't say for sure - but I'm really straining to think of what you've got there.

What's interesting is that in the photo it doesn't appear torn so it adds in my mind to the mystery of what it is. Every time I think of something I wind up with the next thought being - but the screen should have picked that up. Which makes me wonder - is your oil screen compromised somehow?

In any event, good for you that it showed up where it did - could have been a lot worse.

Dan
 
The gasket is too big to pass through the smaller hole to get into the engine. With the gasket the ball can seal better. But, when it breaks it can jam the ball and creates a gap to allow oil flowing through (lower the oil pressure). The design is for metal (ball) to metal (valve seat) contact. Don't know why we have this gasket in between.
 
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