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Old 06-07-2021, 10:36 PM
tom paul's Avatar
tom paul tom paul is offline
Join Date: Aug 2017
Location: Brooklyn
Posts: 13
Default Low Oil Pressure today in my RV7A

I've had the plane about a week. It has a Titan IOX-360-A4H1N.
All looked good on start, run-up, take off and initial cruise, but after doing some flight review maneuvers, such as slow flight, stalls, steep turns, I noticed that the oil pressure was at 55, with manifold pressure up around 22 and tach about the same. It quickly dropped to 50, at which point we decided to return to the field and land asap. The oil pressure snuck back up to 55 or 58 on the way home, but never got into a more comfortable zone.
I am now beginning the process of diagnosing and research. I pray that I am not due for a rebuild or something else very pricey. The engine has just over 1200 hours on it.
There are six quarts of AeroShell 20-50 in the engine.
The prior owner has advised that an oil and filter change might correct it. It has been about 43 hours since the last oil and filter change.
I am looking for advice on how to diagnose the issue, and potentially trace it to a sender/gauge issue. Worst case, it points to a need for a rebuild, and while I truly hope that isn't the case, I do want to be safe, as I fly out of an airport with no places to land on climb out, so I need to minimize the risk of engine failure.
I cheated and bought a flying one!
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Old 06-08-2021, 12:35 AM
bruceh's Avatar
bruceh bruceh is offline
Join Date: Mar 2008
Location: Ramona, CA
Posts: 2,493

Do you have an engine monitor where the data can be downloaded? If so, check the data and see if this is normal behavior, or something new. You can upload data to savvyanalysis for free and see all of the prior flights.

The pressure relief valve can be adjusted with adding washers to increase the oil pressure.
Bruce Hill
RV-9A N5771H flown over 900 hours!
APRS Tracking for KJ6YRP and Flying Over the Hills Blog
2021 VAF donator
EAA Tech Counselor, Pre Buys, Build assistance - canopy/tanks/fiberglass/electrical/repairs
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Old 06-08-2021, 06:40 AM
mahlon_r mahlon_r is offline
Join Date: Jan 2005
Posts: 1,056

What was the oil temperature when the pressure was low? High oil temp will cause the pressure to drop. Was the pressure ok on previous flight?
Good Luck,
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
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Old 06-08-2021, 07:01 AM
lr172 lr172 is offline
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,539

likely culprits are a bad saender or wiring isssues between sender and gauges. Best bet is to install a mechanical, non electric oil pressure gauge and test fly to rule in or out actual low pressure in the engine.

About a 0% chance that an oil and filter change will resolve it.

Do you have enough time to know the normal pressures? Are they low across the board? If 20 psi low at cruise, idle would likely be very low if the pump was going.
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019

Last edited by lr172 : 06-08-2021 at 07:07 AM.
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Old 06-08-2021, 10:37 AM
jrs14855 jrs14855 is offline
Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,592
Default Oil Pressure

The type of oil pressure sender that I have depends on a good ground. I have the ground wire hose clamped to the sender and then direct to airframe ground. Poor ground and also low voltage will cause oil pressure to read low. Best to test with mechanical gage but no need to fly to do that. Correct whatever issue you have before further flight.
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Old 06-08-2021, 11:05 AM
moosepileit moosepileit is offline
Join Date: Dec 2010
Location: Louisville, KY
Posts: 734

There are a host of possible mechanical failures and faulty indication creators.

It's tough on a newish to you plane.

Let's assume, for starters, nothing is newly broken or just wore out at purchase. Look at the logs. Does the "Summer" oil show as 50 weight/100W? How old is the current oil in months for 43 hours?

The last owner may have not changed from multigrade, which some feel gives less summer cooling. Maybe that's what "change oil and filter" meant. Check the logs.

If your checkout flying overcame the oil cooling capacity and got hot enough, pressure goes down more as you then reduce power to return and land until oil temps cool off. Idle oil pressure warm, cool and hot tell a lot about engines over time, not just in one flight.

Knowing your normal temp/pressure relationship will come in time.

Could need to adjust the oil pressure regulation, could have gotten your flexible baffles misplaced/lost some sealing when last recowling the plane, could have lost proper oil cooler airflow, could be a worn vernatherm or its seat or engine bearings or a stack up of wear combination.

Start in the logs- does the engine oil change from winter multigrade to summer single weight, historically?

Multigrade might be ok at normal flight cross country profile or just flying patterns, but doing a checkout you got the oil hot enough the pressure started to fall. Too slow, too much power vs cooling air, too little exit area, marginal cooler BTU capacity- plane could just normally have marginal/improveable oil pressures/temps.

An oil change to 100W and checking the cut open filter for metals doesn't mean you won't still find what is normal vs acceptable vs worn or needing improvement. It does make a difference in summer, to some and may help going single grade oil.

Did you cut and examine a filter before purchase? Is the multigrade fresh or aged?

AeroShell multigrade is 15W50. Many swear BY and others swear AT it in summer. Those swearing AT it use single weight oil in summer heat.

Phillips is 20W50 in multigrade. Its users seem to stick with it year round, I am one of them, a convert from the Shell dance seasonally to Phillips Victory 20W50 AW year round. I'd use whatever was in the logbook during summer season, for now. Same for oil filter manufacture and part number- baseline from the logbooks for now.

Assuming you can read history in the logs, hopefully changed oil/filter in a prepurchase inspection and no making metal is newly found, your oil pump and idler gears are intact, suction screen clear, all FWF conditions are normal and proper- it might just not enough excess oil cooling for slow speed, extended flight as-is on multigrade. Big assumption, but somewhere to start. Can you find local experienced RV type builders/mechanics?

Like Larry said, it's not truly fixed with an oil and filter change alone. Hopefully you found the limits of heat in the oil cooling system as-is and not an engine issue. You might gain some margin with single weight oil, but that alone is not the full story. It could help restore a normal pulse and blood pressure on the new purchase, then systematically find the updates needed as true cures.

How was it from SoCal to NJ? Did you fly it or have ferried? What were the OP/OT trends? Could it climb max power to 10000' and keep oil temp under say 210 degrees?

Has the oil pressure been rock solid? With electric senders they are good til they are not, could be 1000 hours, can be 40 hours. I've done a bunch of edits, and like Tom says below, the gauge/sender is the easiest to rule out with a temp or added mechanical.
RV-6, bought from builder.
O-320, slider, carb, mags, FP

Last edited by moosepileit : 06-08-2021 at 05:08 PM.
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Old 06-08-2021, 12:16 PM
TS Flightlines TS Flightlines is offline
Join Date: Apr 2010
Location: Ridgeland, SC
Posts: 2,893

Tom--When a usually 'normal' pressure fluxation occurs, we tell builders to install a temporary KNOWN good mechanical gauge in the system, usually with a tee off the supply side. This isolates the electrical sender, and gives a second reading to compare. If the 2 readings are the same and low, then look for a mechanical issue. If the mechanicl gauge reads more correctly and the electrical is wierd, then look for something electrical --ground, power, even the sender itself.

I defer to the electrical gurus on VAF for more info on that part.
Tom Swearengen, TS Flightlines LLC, AS Flightlines
Joint Venture with Aircraft Specialty
Teflon Hose Assemblies for Experimentals
Proud Vendor for RV1, Donator to VAF
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Ridgeland, SC,
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Old 06-08-2021, 09:18 PM
cajunwings cajunwings is offline
Join Date: Jun 2007
Location: new iberia la
Posts: 858
Default Oil pressure

I always start with a mechanical gauge plumbed into the existing oil pressure line between the engine and the sending unit. Those results will dictate your next move. Agree with the others that oil and filter change is not going to make much of a difference.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
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Old 06-09-2021, 12:07 AM
Georges G Georges G is offline
Join Date: Apr 2013
Location: FRANCE
Posts: 21

After 150h on the engine I notice fluctuations on my oil pressure (I have an electrical and a second mechanical uma gauge).
I found some dirt on the ball of the relief valve (look like plastic debris).
After cleaning the ball oil pressure came back to normal.
Georges Grenet
RV 14a n? 140054
flying since June 2018
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Old 06-09-2021, 05:37 AM
RVDan RVDan is offline
Join Date: Jun 2012
Location: Frederick, MD
Posts: 940

Originally Posted by tom paul View Post
I've had the plane about a week. It has a Titan IOX-360-A4H1N.
All looked good on start, run-up, take off and initial cruise, but after doing some flight review maneuvers, such as slow flight, stalls, steep turns, I noticed that the oil pressure was at 55, with manifold pressure up around 22 and tach about the same. It quickly dropped to 50, at which point we decided to return to the field and land asap. The oil pressure snuck back up to 55 or 58 on the way home, but never got into a more comfortable zone. .
As someone else asked, what was the oil temp? The RVís with a 360 in them donít like slow flying and maneuvering at low airspeeds when it is warm to hot outside. The oil temp gets hot, oil pressure will drop. Since you didnít mention oil temp in the OP, my guess that it may have been high. There is a direct relationship between oil temp and pressure when the oil is hot. In my -6, with a 360 engine, oil temp has to be monitored when doing low speed maneuvers, slow flight, stalls, low speed turns and so on, for more than a couple of minutes.
Dan Morris
Frederick, MD
Hph 304CZ
RV6 built and sold
N199EC RV6A flying
Retired Aerospace Engineer and A&P/IA
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