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-   -   Oil Pressure Fluctuating Wildly (https://vansairforce.net/community/showthread.php?t=169987)

Towline 03-26-2019 04:08 AM

Oil Pressure Fluctuating Wildly
 
Flying home a couple of days ago, I noticed the oil pressure light flashing high on my OPT-1 from EI.

Panic slightly... then it returns to normal for a bit and then drops to low (literally zero on the readout). Then back to high (120+). Edited to say at this point I thought the only reliable thing I can maintain my concentration on is the oil temp, which remained solid thoughout.

Luckily I was 15 minutes from home so throttled back a bit and it seemed to stay in the normal range, until I powered back to land (dropped down low again).

On landing, no oil loss, no signs of leaks and as said the oil temp remained absolutely constant throughout.

I'm runnning an O-320 D1A with fixed prop and no inverted systems. Oil change about 4 hours (4 weeks) ago. I've noted that it might be worth checking the ball in the relief valve. Just wondered if anybody has had problems with these transducers that might cause such erratic readouts? I've got a licenced eng doing some troubleshooting on it.

Skid 03-26-2019 06:53 AM

Erratic Oil Pressure
 
You did not state what type of transducer you are using. Assuming it is a VDO type check to ensure the ground is good. The units ground through the case so an easy way to check it is to use a hose clamp and clamp a wire to the housing and connect it to a grounding point, then go fly.
I had the same problem years ago.

Towline 03-26-2019 07:28 AM

I think it's a PT-100GA, will check again later when I'm at the hangar.

jabarr 03-26-2019 07:37 AM

Sounds like it may be just indication but PLEASE don?t fly it until pressure is checked with a direct reading gauge.

Towline 03-26-2019 07:52 AM

Yeah roger that. Our engineer has said the same, for me to check grounding on the transducer.

Breezy 03-26-2019 08:48 AM

Had a customer call with this very issue. We went down the same suggestions posted here, all are good. He is based a 40 min flight away so it was difficult to troubleshoot.
I suggested he add another qt of oil and the fluctuations went away. It seems under the right circumstances cavitation can occur at the oil pick up in the sump.
If nothing else it's a cheap place to start.
Cheers!

jrs14855 03-26-2019 01:22 PM

Oil Pressure
 
Minimum oil quantity for most four cylinder parallel valve Lycoming's is 2 quarts. I don't accept thee premise that adding one quart of oil would make wild oil pressure fluctuations go away, unless the oil level was down to one quart.

lr172 03-26-2019 01:48 PM

Quote:

Originally Posted by jrs14855 (Post 1334673)
Minimum oil quantity for most four cylinder parallel valve Lycoming's is 2 quarts. I don't accept thee premise that adding one quart of oil would make wild oil pressure fluctuations go away, unless the oil level was down to one quart.

Agreed. Cavitation typically results in ongoing pressure swings more in the 25%-50% range and not a momentary, complete loss of pressure. Assuming a minimal oil level of course, though there is really nothing to create cavitation unless overfilled. Sucking in air momentarilly (which is NOT cavitation) when oil level is very low, will create this type of indication, but I also think that level is close to 1-1.5 quart.

Instrumentation is far more likely for this type of presentation, assuming a full sump. A single occurence of an immediate pressure loss with immediate reversal is just not a marker of typical oil pressure problems, other than the low oil situation mentioned above.

Larry

jrs14855 03-26-2019 02:27 PM

Oil Pressure
 
For those who are not familiar Pitts Aircraft usually have a bolt on inverted oil system that was originally marketed by Christen Industries. Aviat now controls the former Christen products. Sometimes a new port is welded to the bottom of the sump.
Under certain conditions this system will result in a momentary loss of oil pressure. This is typically down to the 25# range and will immediately recover to normal with no additional fluctuations. This is caused by the ball in the three way valve not being seated in zero G conditions.
A separate issue is that in a sustained 90 degree left wing down bank the oil pressure will go to Zero. If the bank is to the right the oil pressure stays normal.

Aviaman 08-20-2019 01:29 PM

Oil pressure fluctuating, then to zero
 
Following a normal run up, I took off for a short flight to my home airport. After a few minutes I noticed my oil pressure dropping, then rising a bit, then dropping more. Finally it dropped to 0. Very alarmed I landed at an airport I happened to be near. During all this there were no other abnormalities, sounds or indications. After landing, I suspected the pressure sender or wiring to the EFIS. I removed the VDO sender, banged on it a little, wiggled wires, then reinstalled the VDO. I restarted the engine and oil pressure came up perfectly normal. I reasoned this was a sensor problem, not a true oil pressure loss. I took off again, with only about 15 mins remaining on my return leg home. Then, a few minutes after taking off, the same thing happened again, fluctuations followed by 0 oil pressure indication. I flew on home. Again no other abnormality. I haven?t yet determined the problem. I have ordered a mechanical oil pressure gauge to see what?s going on.

This occurred on a very hot day, about 93F. Yet the oil temp was indicating 185F , not really that hot, assuming a correct instrument. I?ve seen hotter with no adverse effects. Is there any scenario where high oil temp could cause this kind of problem? Any other ideas ?


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