What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Low Oil Pressure today in my RV7A

Oil pressure

Got rid of Shell multi-grade 1100 hours ago and never had another problem. Live in Texas, but have flown from Key West to Anchorage on Aeroshell 100. For me problem solved.
 
switching to single-grade

Got rid of Shell multi-grade 1100 hours ago and never had another problem. Live in Texas, but have flown from Key West to Anchorage on Aeroshell 100. For me problem solved.

Thanks Texdog. I just read the recommendations on the Savvy Aircraft page. It seems that single viscosity pure mineral oil is clearly the best for my application, especially since I live in a very humid area and sometimes weeks go by between flights or engine starts. I am only ten hours into this phillips oil, but next chance i get, I will drain it and put in AS100 (with Camgaurd and a new filter, of course). I bought some crush washers, so I will check the filter screen as well.
 
Based on your information concerning the date of the assembly of your ECI Titan / Eagle XP engine kit I would immediately bore scope the cylinders. My RV-8 had these very symptoms with the exact same engine. You see, that vintage of ECI Titan cylinders had a run of bad nickel coating in the cylinder walls. This was due to surface contamination at the factory prior to plating. It triggered an AD. So by all means take a look at your cylinder walls. Then look up the Titan cylinder AD and check your cylinder assembly serial numbers. There were group “A” and group “B” cylinders based on serial numbers. The serial numbers should be in the engine logs or laser etched on the base of the cylinders. Unfortunately ECI Titan did not treat the experimental engine owners the same as type certificated engine owners. ECI warranty on Type Certificated airplanes was replacement, per AD mandate. On experimentals they had the owner remove the cylinders and send them in to the factory where they reworked the cylinders. Then sent them back to the owner. The FAA forbade the rework on Type Certificated aircraft where the cylinders were deemed unairworthy and to be discarded. My engine had cylinders that the factory reworked in lieu of replacement.

Had I known about the issues earlier I would have replaced all the ECI Titan cylinders with new assemblies immediately after purchasing the aircraft.

In my case the cylinder nickel plating came off and got around the rings, scarring the cylinder walls and sendings nickel particles into the bottom end. Based on that elected to do a full TDI / major with new through-hardened steel Superior cylinder assemblies. I sent the engine to Barrett Performance in Tulsa. I always wanted a Barrett engine. Upon tear down they found case fretting indicative of Americas Aircraft not properly torquing the through studs and case half bolts. That had nothing to do with the original symptoms but was a good thing to find during the process. While the engine was out I flushed the oil cooler and had a prop shop flush and reseal the propeller.

I hope your problem isn’t like my problem and is something simple. As it can get $$$. My engine now runs like the proverbial Swiss watch and pulls harder. Barrett dynoed it at 190hp. I attribute the end results to the great break in that comes with steel cylinders along with Barrett’s dyno runs.

I had a whole thread on this back in 2017 or 2018 with photos.
 
Last edited:
Temperature vs kinematic viscosity, Aeroshell 100W vs 15-50 multigrade. For clarity, I've removed the plot lines for Sport, 120W, Diesel, etc, and inserted color. The original is found in the Aeroshell Book:

https://www.shell.com/business-cust...da955d588ce5/theaeroshellbook-edition2021.pdf

By design, single and multi-grades have the same viscosity at 100C/212F. A single grade oil boosts oil pressure only at some lower temperature. Within the typical cruise operating range, the difference is not large.

Note the synthetic component in Aeroshell's multigrade will tend to maintain viscosity with operating hours, while a mineral base oil will lose viscosity. Out near oil change time, viscosity at a typical 190F will be very close.
.
 

Attachments

  • Aeroshell 15-50 vs 100W.jpg
    Aeroshell 15-50 vs 100W.jpg
    48.4 KB · Views: 178
I have same problem!

Hi Tom. Did you ever figure out the cause? I have the EXACT same problem. Start up and beginning of flight, OP is in the mid 80's. After take off, it slowly, but predictably starts to drop and by mid flight, it's in the mid 50-60psi range. If I fly hard (acro, full throttle), it drops much more quickly, but so far (until last weekend) has always stayed above 50psi, so I wasn't worried enough to stop flying. If I reduced power to 2100rpm or less, oil pressure quickly goes back up. Within about 5-10 seconds of reducing power, I'll gain 5psi or more. If I kept it reduced or pull back to idle (like going back to land), OP will continue going back up and by the time I land, I'm back in the 70psi range.

I have ruled out faulty sender, engine monitor, etc. Oil cooler was removed, and flushed. No obvious clogs or debris found. Vernatherm was removed and tested to be working. Hoses are clear, not kinked. Sump screen clean. Oil analysis has always come back good, but I did not do oil analysis the last two oil changes.

I have a fuel injected O320, slightly modified, FP prop, Raven inverted oil system. Oil is Phillips 66 100AW.

So what is it that would cause low oil pressure, but only at high throttle settings?? (or at least it's worse at high throttle settings and gets better with reduced throttle)
 
Last edited:
What make and type sump do you have?
My Titan IOX-370 cold air sump requires more oil than I was used to with my old standard Lyc sump O-360.
My "tell" was oil pressure would go up if I was pulling G. (forcing more oil to the pickup area). Apparently, it was the old soda straw in the empty cup syndrome.
 
Hi Tom. Did you ever figure out the cause? I have the EXACT same problem. Start up and beginning of flight, OP is in the mid 80's. After take off, it slowly, but predictably starts to drop and by mid flight, it's in the mid 50-60psi range. If I fly hard (acro, full throttle), it drops much more quickly, but so far (until last weekend) has always stayed above 50psi, so I wasn't worried enough to stop flying. If I reduced power to 2100rpm or less, oil pressure quickly goes back up. Within about 5-10 seconds of reducing power, I'll gain 5psi or more. If I kept it reduced or pull back to idle (like going back to land), OP will continue going back up and by the time I land, I'm back in the 70psi range.

I have ruled out faulty sender, engine monitor, etc. Oil cooler was removed, and flushed. No obvious clogs or debris found. Vernatherm was removed and tested to be working. Hoses are clear, not kinked. Sump screen clean. Oil analysis has always come back good, but I did not do oil analysis the last two oil changes.

I have a fuel injected O320, slightly modified, FP prop, inverted oil and fuel. Oil is Phillips 66 100AW.

So what is it that would cause low oil pressure, but only at high throttle settings?? (or at least it's worse at high throttle settings and gets better with reduced throttle)

In my experience a mismatch between case and oil pressure regulator housing will cause this odd behavior. The ball that regulates OP must float inside of a cage to work properly (keeps ball centered over flared hole in case). Old crankcases have the cage on the case and the newer ones have the cage on the housing and they accordingly have different housings to match. If you put the uncaged housing on the uncaged case, the ball will hold ok untill the volume goes way up at high power and then it falls off to the side and pressure drops accordingly as now it is bleeding too much oil off. Most A&Ps dont seem to know this. The 540 core that I bought was set up like that and struggled to understand why pressure dropped at high RPM, where it shouldn't. Mahlon pointed out this potential mismatch issue. He is a rock star! You will need to pull the regulator and see if there is a cage on the case. Mahlon has a post explaining the differences in looks of the two different housings- derby hat (cage on the case) vs abe lincoln hat (no cage on the case). The abe lincoln hat won't fit on a caged case, so if you have that style you don't have a mismatch IIRC.

Larry
 
Last edited:
What make and type sump do you have?
My Titan IOX-370 cold air sump requires more oil than I was used to with my old standard Lyc sump O-360.
My "tell" was oil pressure would go up if I was pulling G. (forcing more oil to the pickup area). Apparently, it was the old soda straw in the empty cup syndrome.

I just have the standard Lycoming sump for the O320 with the horizontal sump screen. I don't think that's the issue.
 
In my experience a mismatch between case and oil pressure regulator housing will cause this odd behavior. The ball that regulates OP must float inside of a cage to work properly (keeps ball centered over flared hole in case). Old crankcases have the cage on the case and the newer ones have the cage on the housing and they accordingly have different housings to match. If you put the uncaged housing on the uncaged case, the ball will hold ok untill the volume goes way up at high power and then it falls off to the side and pressure drops accordingly as now it is bleeding too much oil off. Most A&Ps dont seem to know this. The 540 core that I bought was set up like that and struggled to understand why pressure dropped at high RPM, where it shouldn't. Mahlon pointed out this potential mismatch issue. He is a rock star! You will need to pull the regulator and see if there is a cage on the case. Mahlon has a post explaining the differences in looks of the two different housings- derby hat (cage on the case) vs abe lincoln hat (no cage on the case). The abe lincoln hat won't fit on a caged case, so if you have that style you don't have a mismatch IIRC.

Larry

My pressure relief valve is the correct one for the case. No mismatch.

I have the Raven inverted oil system and was thinking that that possibly could be causing air to be introduced into the system and cause cavitation of the oil, which gets worse with higher RPMs?? Why this is not a problem with everyone who is using it, I don't know. I'm just throwing out ideas. One of the lines that go to the top of the oil valve (for oil to return to the sump when inverted) comes from the top of the case where the old vacuum pump would normally go. There's a gear that's turning and maybe it's agitating the oil and introducing air into the system and causing low OP?? This would explain why it's worse at higher RPMs? (but the relationship between RPM and oil pressure only holds when the pressure has dropped to very low levels - low 50's)

Would an oil pump that is starting to go bad cause this problem? (low oil pressure at high RPMs and high oil temps) If the gears in the oil pump are starting to wear, my thinking is that at higher RPMs, it's turning faster, but not moving as much oil, but instead just introducing air bubbles into the oil. This is why oil pressure drops with higher RPMs (and at lower RPMs, it's not as bad). But this would mean that there is a pretty direct relationship between RPM and oil pressure. But this is not my observation/ experience. What I am seeing is that if oil pressure drops very low (low 50s/ high 40s), then pulling back the throttle helps to increase pressure. BUT if oil pressure is already high (60psi and up), pulling back the throttle doesn't do anything. Also, if oil temperature is low (below 180-190), oil pressure does not go below 60psi. So it's a combination of things. And the relationships are not linear. Very puzzling...

I flew again today and same pattern. Take off/ beginning of flight low to mid 80psi, oil temp starts low and within about 10 minutes rises to about 180F. During these 10 minutes oil pressure drops into the low 70's/ high 60's. After that oil temp goes a little above 190F and pressure drops into the high 50psi range. If I pull back throttle to about 2200rpm, pressure comes back up into the 60psi range. Coming back to land, I pull back throttle to idle, and pressure continues to go back up. By the time I'm on the ground and ready to shut down, pressure is back up to 81psi.

Raven inverted oil diagrams: https://ravenaircraft.files.wordpress.com/2014/12/raven-inverted-diagrams.pdf
 
Last edited:
Never saw an oil pump that was worn enough to cause any problems pressure at RPM. sometime a little low at low rpms but never any issues at high rpms. They can be really messed up from camshafts going bad and you never see any issues with oil pressure at rpm. I would totally discount a worn pump.
If it were me, I would get a hold of a normal oil pick up screen and cap and install them and plug off the raven three way valve and fly it as a normal non acro engine to eliminate the entire acro system. To me, you need to determine if the problem is the Raven system or the engine first, before pursuing anything else.
I assume that you have confirmed that the oil pressure is doing what you say with a direct reding gauge as well.
Good Luck,
Mahlon
 
I am with Mahlon. In all my years in auto, I have NEVER seen a pump with good pressure at low RPM and poor at High RPM. Failure is almost universally observed first at low RPM with a bad pump. My feeling is that it is extremely unlikely that the reverse could happen with a bad pump. The Lyc pumps are very similar to auto pumps, at least the older ones. Air ingestion upstream of the pump will cause lower pressures, but struggle to see how that could only happen at high RPMs, though I have never seen or studied a raven system and therefore cannot speculate if or how it could cause that. But is would seem that you could be on the right track, as not too many faults will cause your symptoms. I would do as Mahlon suggested as it should confirm or reject your hypothesis.

Larry
 
Last edited:
Never saw an oil pump that was worn enough to cause any problems pressure at RPM. sometime a little low at low rpms but never any issues at high rpms. They can be really messed up from camshafts going bad and you never see any issues with oil pressure at rpm. I would totally discount a worn pump.
If it were me, I would get a hold of a normal oil pick up screen and cap and install them and plug off the raven three way valve and fly it as a normal non acro engine to eliminate the entire acro system. To me, you need to determine if the problem is the Raven system or the engine first, before pursuing anything else.
I assume that you have confirmed that the oil pressure is doing what you say with a direct reding gauge as well.
Good Luck,
Mahlon

Thanks! I was thinking the same, but have been reluctant to do it. Part of my hesitation is that the original screen had to be cut and a new fitting installed (instead of the plug) when I installed the Raven. So I'll either need to find a new screen or find a way to plug the hose/ fitting from the Raven.
 
cause of problem found!

I disconnected my inverted system and test flew and oil pressure problem went away. Pressure was rock solid in the normal range. With higher RPM, oil pressure was slightly higher (as you would expect) - unlike what I was experiencing before.

Then I took apart my inverted oil system and inspected every part carefully. I could not find anything obviously wrong - no kinks or obstructions in the hoses, the balls in the valve were moving freely, no grime and nothing looked excessively dirty or out of place. Everything was installed per instructions. Then I looked inside the hoses and found that one of the hoses had two blisters on the inner wall! It's not easy to see b/c it's dark inside the hoses and unless you pull the hose perfectly straight and point it towards the sky (or shine a light through the other end), you can't see anything.

Anyway, that's what's obstructing oil flow. I'm buying new hoses and will put everything back together and hopefully that will solve the problem.

Here's a photo of the blisters on the inner wall of the hose. Hope this link works. I haven't had a lot of luck posting photos in the past.

view
 
Propeller type

1flyingyogi, what kind of propeller do you have, a standard CS or an aerobatic counter-weight type?
 
There have been cases with brake lines with the hose swelling to the point that the hose lets pressure through when braking and then hardly releases the pressure at all with the result that the brakes dragged something terrible. New hose solved the problem.
 
Hose autopsy

Here's what the cross section of the hose looks like. The inside rubber part pulled away completely from the outer SS braid. Bad quality hose. I got them from Summit Racing, but don't remember the brand. I'm replacing with Aeroquip SS braided ones.

hose-cross-section2.md.jpeg


hose-cross-section.md.jpeg
 
Jumping in on this thread as my issue mimics the original one.

Going into Oshkosh last Friday, when I throttled back to transition at Green Lake, my Oil Pressure dropped into a 45-49 range. Adjusting throttle, my OP would rise to normal range, low throttle, back to 40s. Suspecting the OP sender, I changed it out while at HBC. Upon startup yesterday to taxi out, low pressure once again. It wasn't the sender.
On a quick runup, higher rpm brought it back into the normal range. I decided to takeoff with the intentions on returning if the low rpm persisted. It was in normal range. My original plan was to fly to Washington state, but decided to head home to NC where I could properly troubleshoot. RPM enroute, although still low, were ~62. Throttling back to descend, RPMs went down to 45ish. CHT & EGT temps where normal.

My next course of action would be to check the relief valve & the suction screen.
Any recommendations would be appreciated.
I'm running a Superior IO360 900+TT & never had low OP issues prior.

Update: Problem resolved. I removed the relief valve & no noticeable debris. Cleaned it up, new crush washer…
Oil pressure now in normal range , 62 at idle.
 
Last edited:
I spoke too soon.
Yesterday, I only did a taxi & runup with the cowling off. OP was good.

Todays test flight at startup & various throttle settings
OP-OT-RPM
62-104-1050 at startup to taxi
74-129-2270 in flight
71-168-2510
65-188-2240
41-192-1130 landed & taxi back

CHTs 363,364,364,365 in flight
EGTs 1370-1397

I'm draining the oil & will check the suction screen next.

Question regarding the pressure relief spring.
Do the springs lose tension & have to adjusted over time?

Any other suggestions appreciated.

Note:I'll be downloading the data later today.
 
Last edited:
41 at idle after flight (with hot oil) isn’t a problem.. the lower limit I believe is 25psi. Bring up the RPM to runup rpm.. is it above 55? Fly it again.

I had oil pressure low, I replaced the sensor from a VDO knockoff from Amazon, still the same. I put a known mechanical gauge teed into the line and had a good reading on the mechanical. I then get a good VDO sender, and it’s all better.

One thing I noticed that before start, the bad senders were indicating 10 psi before start..
 
I spoke too soon.
Yesterday, I only did a taxi & runup with the cowling off. OP was good.

Todays test flight at startup & various throttle settings
OP-OT-RPM
62-104-1050 at startup to taxi
74-129-2270 in flight
71-168-2510
65-188-2240
41-192-1130 landed & taxi back

CHTs 363,364,364,365 in flight
EGTs 1370-1397

I'm draining the oil & will check the suction screen next.

Question regarding the pressure relief spring.
Do the springs lose tension & have to adjusted over time?

Any other suggestions appreciated.

Note:I'll be downloading the data later today.

Given the intermittent nature of the problem, I don't think you will find the problem in the pressure relief mechanism. Yes, springs can lose tension, but it will be very consistent. While 41 at idle isn't low per se, if that is 10 or 20 PSI lower than it was a month ago at the same OT and RPM, that is a SERIOUS issue that must be identified and addressed. OP can slowly drop over long periods due to wear and other issues, but a significant drop in OP out of the blue is cause for serious concern. Not enough data here to speculate further, but cleaning out the sump screen would be the very next thing I did if you haven't already.

Above states that at 2240 & 190 OT you are getting 65 PSI. What pressure were you getting at 2240/190 in the past? If my 190* idle oil pressure when new was 60 and over 2000 hours dropped to 40, I would not be highly concerned. However if that 190* idle oil pressure dropped from 50 to 40 across a few flights, I WOULD NOT take that plane back into the air. Rapid changes in oil pressure with otherwise constant variables (i.e. RPM and OT) is a sign of failure and can go down hill VERY rapidly. It could be an issue with the pressure relief, but could also be a bearing coming apart or an oil pump self-destructing. Please proceed with caution.
 
Last edited:
Back
Top