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Sudden temporary change in oil pressure

jdeas

Well Known Member
On a flight last week I had a -19psi change in my oil pressure, the majority of change in 6 seconds!

No alarms sounded as the oil pressure was still in range but picked up on it and made an immediate turn to more favorable landing zones as it was still slowly trending down. During the turn I was also changing power settings and looking for oil when I noticed the pressure coming back up! Located a safe path to the nearest airport but the pressure was rock solid from then on. On landing the oil level was at 5.5q, about where expected so there was no unexplained oil loss. The event lasted over a minute and I see nothing in the data that would suggest this was instrumentation.
The only conclusion I can reach is the oil pressure regulator must have gotten something on the seat or just didn't seat properly until I shook it loose with power and g load. Weird considering this was 10+ minutes after establishing a climb profile.
I attached the Savvy flight (11 minutes in) for those who may have more insight into this anomaly.
https://apps.savvyaviation.com/flights/4230664/d5d74d4f-db1f-4232-881e-b277f8b8505e
 
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Yup, I flew the other day (Lyc O-360) and the oil pressure was about 10-12 psi higher than I usually see. After landing I tapped on the housing for the regulator ball. Next flight it was back to normal.
 
On a flight last week I had a -19psi change in my oil pressure, the majority of change in 6 seconds!

No alarms sounded as the oil pressure was still in range but picked up on it and made an immediate turn to more favorable landing zones as it was still slowly trending down. During the turn I was also changing power settings and looking for oil when I noticed the pressure coming back up! Located a safe path to the nearest airport but the pressure was rock solid from then on. On landing the oil level was at 5.5q, about where expected so there was no unexplained oil loss. The event lasted over a minute and I see nothing in the data that would suggest this was instrumentation.
The only conclusion I can reach is the oil pressure regulator must have gotten something on the seat or just didn't seat properly until I shook it loose with power and g load. Weird considering this was 10+ minutes after establishing a climb profile.
I attached the Savvy flight (11 minutes in) for those who may have more insight into this anomaly.
https://apps.savvyaviation.com/flights/4230664/d5d74d4f-db1f-4232-881e-b277f8b8505e

Unless you have a good deal of bearing wear, the ball should be well off the seat at 2400 RPM. Improper seating, due to debris, in the ball seat area, at those RPMs, is a pretty unlikely reason for a low pressure indication. A problem with the cage or spring could cause that though. My engine had the wrong adapter (i.e. no cage present) and the pressure would fall only at high RPMs (ball was falling off to the side). Further, typical sendor errors and anamolies usually report high vs low readings. While a bad sender or wiring issue is absolutely possible, I would keep a close eye on it to confirm it is not a mechanical issue.

Larry
 
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What type of oil pressure sensor? Dynon recently issued a service bulletin for the Kavlico sensors.
 
Here's the affect a piece of debris in the relief valve seat has on oil pressure. Larry is right, your observation does not seem to fit debris in the seat.
 
Low PSI

Guys,
Thanks for the input. This is a one time anomaly after almost 500hrs of use. The engine is far from new so no idea how far the ball is off the seat at 2400.


A point of reference, Switched to 120wt oil and removed a washer from the regulator around 20hrs ago. It has given me more consistent psi but perhaps the regulator is not quite happy with the washer/spring stack and/or missing the cage.
This is the tall hat fixed regulator. I'll have to see if a cage should be there.
 
Guys,
Thanks for the input. This is a one time anomaly after almost 500hrs of use.

Please don't take comfort in that. Most engines will go 1000's of hours without ever having an indication like this. It may be something simple like a loose connector. However, your engine is whispering to you, please don't ignore it. A failed oil system, typically results in a very bad day.

You need to find the cause.

Larry
 
Please don't take comfort in that. Most engines will go 1000's of hours without ever having an indication like this. It may be something simple like a loose connector. However, your engine is whispering to you, please don't ignore it. A failed oil system, typically results in a very bad day.

You need to find the cause.

Larry

Point taken, BUT sometimes “it just is”. I had a 20+ psi drop for a few flights and added a quart of oil and it took care of the OP drop. Pressure has been back to normal since. On here I was told that adding oil wouldn’t solve the OP issue and something else is wrong. Well, it did and there wasn’t. So where I’m going with this is if your OP is back, sometimes it is OK to assume it was a transient excursion and you may never know why, but you can be satisfied that the problem is gone.
 
G
This is the tall hat fixed regulator. I'll have to see if a cage should be there.

Two styles for this. One has the cage on the block, in which case, you need the derby hat style cap(not sure if they ever made an adjustable regulator for this style). The other has no cage on the block and it requires the abe lincoln hat style that has a cage built into the cap. To be clear, I don't believe that this is your issue, as it would have presented a long time ago.

Larry
 
Point taken, BUT sometimes “it just is”. I had a 20+ psi drop for a few flights and added a quart of oil and it took care of the OP drop. Pressure has been back to normal since. On here I was told that adding oil wouldn’t solve the OP issue and something else is wrong. Well, it did and there wasn’t. So where I’m going with this is if your OP is back, sometimes it is OK to assume it was a transient excursion and you may never know why, but you can be satisfied that the problem is gone.

pressure drops that can be tied to a low oil level is a completely different matter and is to be expected. OP stated that he confirmed a proper oil level at the time of the event. No one should ever ignore irregular oil pressure drops. These are remarkably stable systems with VERY FEW intermittent excursions from normal patterns. The exception being instrument/sensor issues.
 
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Testing

Points well taken, the oil was at 5.5 qt, lower than I normally run , nose up climb and hit when the vernatherm would have been transitioning to the oil cooler. The presure regulator was also adjusted and a 120wt oil with no additives used at condition inspection 15 hrs prior.

I plan to do a test flight later this week with the oil level back up to where I normally see it. Being transient, I suspect:
Air pulled into the oil pump (extended climb w/ different oil type and level)
Transition of the vernatherm (filling the oil cooler)
Oil pressure regulation seat (ball off center or debris)

Of these I believe the regulator is the most likely but still looking for feedback. I have 15hrs between the adjustments being made to the system and 40min of flight after the event with no other occurrence in the logs.
 
Points well taken, the oil was at 5.5 qt, lower than I normally run , nose up climb and hit when the vernatherm would have been transitioning to the oil cooler. The presure regulator was also adjusted and a 120wt oil with no additives used at condition inspection 15 hrs prior.

I plan to do a test flight later this week with the oil level back up to where I normally see it. Being transient, I suspect:
Air pulled into the oil pump (extended climb w/ different oil type and level)
Transition of the vernatherm (filling the oil cooler)
Oil pressure regulation seat (ball off center or debris)

Of these I believe the regulator is the most likely but still looking for feedback. I have 15hrs between the adjustments being made to the system and 40min of flight after the event with no other occurrence in the logs.


I run between 4 and 5 quarts in my 320. Never had a momentary drop in 700 hours, except those related to RPM. My vernatherm opens and closes all the time, just like every other lyc. Never a momentary drop.

Larry
 
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You say when you changed power (assuming you reduced power) the oil pressure came back up. Intuitively this is backwards. Except.... This can happen if you have an oil hose that has aged and had it's inner liner delaminate from the steel braiding. So while the hose looks good on the outside, inside you can have that loose section of liner "balloon" out when fast flow causes a pressure drop. The flexible liner basically balloons out due to the pressure drop caused by the flow. It basically gets sucked into the flow causing a restriction. When RPM is decreased the suction reduces and the balloon deflates opening the passageway allowing more flow and a higher pressure reading. If the pressure drop happens after takeoff during cruise then the hose in question is probably one going to the oil cooler where it doesn't enter the picture until the vernatherm closes at around 180 degrees F. I was educated on this by Alan Barrett of Barrett Precision a few years ago.
 
Can not re-create

To be safe I changed the oil filter and cut the old one looking for metal. Nothing was found and after speaking with a couple of local shops, one felt the oil regulator must of not seated properly and cleared, the other shop suggested air in the oil system. Both suggested this was not an issue.

5 hrs later no new events.
 
after speaking with a couple of local shops, one felt the oil regulator must of not seated properly and cleared, the other shop suggested air in the oil system. Both suggested this was not an issue.

5 hrs later no new events.

As mentioned, at high RPMs, the regulator is "ALWAYS" off the seat; Intermittent debris there does not explain your symptoms, though it can explain low pressure at low RPMs. If you are getting air into your oil system at high RPM power settings with 5 quarts in the sump and not upside down, I would argue that you ABSOLUTELY have an issue that needs addressing.

Not arguing that this could not have been a one time occurence. Only encouraging you to not ignore this, as it could return. While I have met some very knowledgeable A&Ps, I have also met many that don't seem to have a solid grasp of engine fundamentals.

Larry
 
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