Oil pressure fluctuation

Hi everybody,

I'm flying a RV7-A with a IO360 A1A since 5 months. Engine has 1500 hours and has been top overhauled before i bought it. It is equipped with a governor and half christen system (oil separator).

I have chrome cylinders and everything above 6-6.5 quarts spits out to the belly.

So i recently made some flights to measure my oil consumption and define what was the "good" oil level for my engine.

During cross-country flight, with 7-8 quarts, i can see a steady constant oil pressure (75 psi). oil consumption is about 0.4qt per hour.

Here is a snapshot of EFIS data for a 7qts cross country flight :



The issue appears when oil level is about 5-5.5 quarts. At this level, Oil pressure drops to 60 psi in average and i can see oil pressure fluctuation during all flight. At the same time, oil consumption is ok (0.1qt/h)

At 5qts :



At 4.5 quarts, oil pressure is 50-55psi in average and can drop to critical level in steady nose down or during bumpy weather. I stopped tests here.

2 things i'm bugged with :
- oil pressure seems to be dependent of oil level, that is very strange to me
- i suspect oil fluctuation means pump sucks air because of "low" oil level. But 6 qts seem not to considered as low level, based on experience of other pilots.

The solution is certainly to fly above 6 qts but i'm keen to understand the root cause of this issue before adding oil.

If anybody has encountered the same situation, I would be happy to hear about it.

Possibility? Piston ring blow-by causing oil foaming. Entrapped air causing pressure fluctuation at lower oil level. Six qts is not low. Even 4 qts should be fine. Chrome cylunders. Does oil turn black quickly?

You definately have something not right going on there, you should be able to run 3-4 qts with no change in oil pressure.

In a proper setup, you really cannot suck air in the feed system until the oil level in the sump reaches the pickup screen. Foaming typically occcurs only from cavitation (rotating crank hits oil as it spins) and I don't believe that the design of the Lycoming will allow this at any normal oil level. Two possibilities to consider. The oil level that you are measuring is at rest. There is no gaurantee that this results in a good level while running, especially when you have equipment in the circuit that was not originally engineered. You mentioned an inverted system. This could be draining into the sump at rest and then gets refilled at startup. This type of scenario would require that you maintain an at rest oil level higher than that of the original design. You would need to measure oil level during engine operation to confirm this or do more engineering to determine a safe at rest oil level. This also applies to large oil coolers that are draining back to the sump at rest.

Second, depending upon the sump feed setup, you could have a pin hole leak that is above the screen/inlet, but below the 7 qt. fill level, and when the oil level drops below this level, you suck air in with the oil, causing erratic pressure levels.

Given your symptoms, I would focus on the items above or related to the oil input, as the problems are directly related to oil level. You should also add oil back to confirm the problem disappears and was not coincidentally related to the oil level. Unless, of course, you have observed this behavior through several cycles.

I would not consider running this engine at less than 7 qts until you figure out the issue.

Larry

With a half system, I'm guessing that your oil pickup and path to the oil pump is unmodified? If so, then are you sucking air ar the oil pan to Accy case connection? That's about the only possible leak source that would be oil level dependant that I can think of. Even that is well above even a "full" sump, so that's a strange one.

FWIW, I consider 6 qts "full" in my 360. I don't add until it gets below 4.

The LA-4-200 Lake Buc uses the IO 360 A1B. As this pusher amphib was designed they are very prop end low- even in level flight. It's oil pressure behaves as you describe and as the graph displays. 8 quarts is fine but don't let them drop below 7.

In the case of an RV I strongly agree with the previous posts from Walt and lr172.

lr172 said:

"Second, depending upon the sump feed setup, you could have a pin hole leak that is above the screen/inlet, but below the 7 qt. fill level, and when the oil level drops below this level, you suck air in with the oil, causing erratic pressure levels."

Larry

Click to expand...

Nicely stated. If air is entrained, it will accelerate cavitation erosion in the main/rod bearings and should be addressed.

Additionally, The pressure also goes opposite that expected with stabilized temperature.

Nothing to add to the diagnostics.

F1R said:

The LA-4-200 Lake Buc uses the IO 360 A1B. As this pusher amphib was designed they are very prop end low- even in level flight. It's oil pressure behaves as you describe and as the graph displays. 8 quarts is fine but don't let them drop below 7.

In the case of an RV I strongly agree with the previous posts from Walt and lr172.

Click to expand...

So, is the oil pickup (suction bell) on this model relocated?

BillL said:

So, is the oil pickup (suction bell) on this model relocated?

Click to expand...

I think he was referring to the fact that the engine is mounted front end low (i.e. unlevel), causing an unlevel oil level. This would expose the suction bell at a level higher than that of an engine mounted level.

I think that i used the word level too many times here

Larry

BillL said:

So, is the oil pickup (suction bell) on this model relocated?

Click to expand...

http://youtu.be/ND6hygMBvlw

Type certified and a factory engine. Over 1000 of these were built. The engine and propellor were angled downward to make the elevator more effective for hauling the AC up onto the step on water take offs.

This thread jogs my memory to an incident Kevin H had with his 8 while flight testing when he kept the nose down exploring the VNE. IIRC he has a 200 HP 360 so it might have a similar sump arrangement.

Hi there,

Yes, i have observed this behavior through several cycles. As soon i add oil to 6.5 quarts and more, i get a steady oil pressure.

Oil is not turning black and compression rates are OK.

Regarding the 2 mentioned points :

1/ Pin hole leak above the screen/inlet, but below the 7 qt

Yes, this could be a very good explanation for fluctuant measures. But i cannot explain why during steady nose down attitude or bumpy weather, my EFIS shows 20 psi for few seconds and loudly warns (scary warning !). When it happens, it really looks like engine is oil starved. Even an abrupt nose down maneuver stopped governor to be feed and made a short over RPM. So i think my oil level was critically low. :-(

2/ oil level measured at rest vs oil level at run.

Do you think governor could use high level of oil when operated ? enough to "empty" sump to a critical level ? I'm using stock MT governor.

I also installed an antisplat aero valve onto exhaust to burn oil coming from breather line (coming from my oil inverter).

Also, I will shortly drain the oil and measure exact quantity of oil at rest and compare it with what dip stick shows.


Anyway, thank you for your very accurate highlights

Cyril

orionis said:

Yes, this could be a very good explanation for fluctuant measures. But i cannot explain why during steady nose down attitude or bumpy weather, my EFIS shows 20 psi for few seconds and loudly warns (scary warning !). When it happens, it really looks like engine is oil starved. Even an abrupt nose down maneuver stopped governor to be feed and made a short over RPM. So i think my oil level was critically low. :-(
Cyril

Click to expand...

You need to figure out the configuration of your oil suction. Mine sucks from a casting in the pan and the hole is toward the rear of the pan. In this config, if I were to only have 1" of oil in the pan and I nosed down, the oil would move to the front of the pan at an angle and expose the opening causing the abrupt and temporary lack or pressure. This would further support the theory of low oil level while running.

I don't know much about CS props. I suspect the governor and hub will hold a decent amount of oil, but I don't know how much. I also don't know if they have check valves to hold the oil in them. I don't believe they do, as I used to cycle the prop in a 182 that I rented to insure the hub was full during runup.

Do you have an oil filter? Do you know if it holds it's oil? A leaking check valve could be causing this to drain back. If that is that case, there is 1/2 a quart that shouldn't be considered in your fill level.

Larry

Hi,

I got this sump :



IO-360-A1A has a wide shallow oil sump and the oil pickup is towards the rear. So it could confirm the low oil alerts in descent for example.

I also suspect half raven installation. My engine blows through breather line, so this means there is pressure in the crankcase.
And my air-oil separator has one plug at a pick-up located under the sump.

I'm thinking about this because during flight, oil pressure increases at G >1 (when i pull the stick).

It could be possible that during operation, pressure in crankcase flow up oil to the christen can. So may be half a qts or may be more is not usable during flight.

I will remove this oil separator to see if it improves. Will report the results here.

cheers

orionis said:

Hi,

I got this sump :

IO-360-A1A has a wide shallow oil sump and the oil pickup is towards the rear. So it could confirm the low oil alerts in descent for example.

I also suspect half raven installation. My engine blows through breather line, so this means there is pressure in the crankcase.
And my air-oil separator has one plug at a pick-up located under the sump.

I'm thinking about this because during flight, oil pressure increases at G >1 (when i pull the stick).

It could be possible that during operation, pressure in crankcase flow up oil to the christen can. So may be half a qts or may be more is not usable during flight.

I will remove this oil separator to see if it improves. Will report the results here.

cheers

Click to expand...

Keep investigating this thing; You'll find it eventually. Your crankcase doesn't really have positive pressure. The blow-by is technically pressure, but it is relieved/equalized via access to atmosphere via the breather. This is not really pressure, as it cannot build. You exhale from your lungs, but the pressure of that event is released and can do no work. Put your lips around a balloon and the captured pressure can do work. The breather is like an opening between your lips and the balloon. Yes, pressure technically exists but it is immediately equalized.

The wide pan is going to require a greater margin of oil quantity. Because so much oil is spread out over an area (i.e. more volume per area) you don't have anywhere near the same margin (as in height above inlet) that I do on my O-320 pan without the wide flares and the plenum structure taking up space.

I think your just going to have to maintain at least 7 Qts as the critical level and deal with the oil loss. Even if you figure this out, it won't likely change this fact. It would be good to confirm that no irregular situation exists, but the engine needs what the engine needs. Be careful when comparing your required oil level with others, as they may not have the same pan as you. Take a look at a standard O-320 pan for comparison.

Good luck,

Larry

I looked up the oil path and realized my question about oil pick up location is fixed for this engine design. Thanks for the gentle nudge to do the proper research.

Back to the OP - When you drain and refill to determine the actual level in the sump, will you be removing the screen and checking for restriction there? That could add to the restriction and either air suction or cavitation on the pump inlet side. Your comment about the +1 G increase in oil pressure, means that the pressure on the inlet, at the suction is greater than 1 G, and might be a clue to your root cause.

If the issue were excessive clearance of the pump gears, or leaking at the sump/case joint, then I would expect +1 G's to lower oil pressure as it has to pull from a higher head.

It might be worth checking that screen before removal of the breather can, or at the same time.

Good luck.

Oil Pressure variation in shallow sump

I read this thread with particular interest and thought I'd add my experience.

I have virtually the same problem with my engine including the odd fluctuation in bumpy air described by Orionis. I wrote a long narrative, shown below, earlier this year which is very much like his problem, but decided not to send it but rather to keep looking for the problem myself.

With the number of responses I've seen, I begin to doubt we all have a pinhole leak. Seems that these wide, shallow sumps have a common performance issue and I still haven?t really decided why. I don?t think anyone else said so, but as noted in my narrative below, I have chrome cylinders and I do believe I?m dealing with some elevated blow-by since the oil gets dark pretty quickly after an oil change.

At any rate, so far, my solution has been to add some washers in the pressure relief valve, add oil to keep the level up, and keep an eye on it. I don?t seem to have that much oil on the belly, either.

Here?s the story I wrote months ago:

I have a curious oil pressure drop when I descend from altitude in my RV7 which now has a little under 70 hours on the engine since it was installed on the airframe. TSMO is about 300 hours. Engine is an IO-360-A1B, Hartzell CS, sump is LW-74384 which some refer to as a ?shallow? sump or the one that has the ?wings?. Governor is an MT, cylinders are chrome. The engine came off a Pitts that was set up for fixed pitch operation, but which I converted back to CS for the RV7 installation. Naturally, the sump had been modified for inverted operation on the Pitts, and, as such, a boss was welded on the rear of the sump to re-route oil when the engine is upright from the sump through the ball valve to the oil pump. It was converted back to non-inverted operation so the weld boss now is plugged off. Oil suction is back to the original design, in other words. I didn?t see it done, but the ?acorn? plug that goes into the original oil pickup finger screen passage must have been removed (if it hadn?t been removed, the engine would?ve been starved for oil on the first start after I removed it from storage).

Oil PSI, Oil Temp, EGT, CHT are all Van?s electric gauges.

Oil usage seems to be about a quart in 4.0 to maybe 5.0 hours or so, but I?m not sure my measurements are final on this yet as I am still trying to pinpoint it.

I usually perform a cruise descent by merely trimming at around 500 feet per minute, richening mixture as needed during the descent.

What happens, in general, is that when the reference mark on the oil stick indicates oil level around the ?6? mark, plus or minus, before departure, I might see the oil pressure, once it's warm, drift from around 75 lbs. down to the low 60?s during such descents. I?m not convinced the ?6? mark means 6 quarts, but it?s a reference.

A more specific example occurring recently begins with the fact that I purposely left the oil at about ⅜ - ? inch below the ?6? mark on the dipstick before departing. I flew for about 1.5 hours, then started descending from 8.5k altitude. Oil pressure before starting the descent was around 75 lbs. Oil temp stayed around 180 and didn?t vary at all ? in fact, it dropped a little during the descent which makes sense. During the descent, O/P began dropping and settled around 60 lbs. or slightly over 60 lbs. during the descent. When I leveled off, oil pressure settled in the upper 50?s. Upon reducing power during the straight in approach, it dropped to mid 40?s, but that might be okay since I had pulled the power back.

Within a minute after shutdown, I decided to perform a hotstart; it started quickly, no problems, and idle oil pressure was up to 62 lbs. with oil temp at 190 (as could be expected with OAT around 85). That seems wrong, too. Can't be right. Idling at 1,000 rpm should show pressure less than 60 lbs when it?s very warm oil we?re talking about. Frustrating, because I wonder if my oil pressure gauge is to blame.

I?ve read and heard several versions of this scenario and it is generally suggested that the oil suction pickup entry point in the sump is unporting, allowing air into the system. I don?t think so. The behavior also suggests that this is what's happening, but on the other hand, the aircraft deck angle during descent doesn?t seem like it would be enough to uncover the port due to the sump oil ?pooling?toward the front of the sump.

In both examples described above, oil temp, CHT & EGT stayed steady. The governor maintained rpm without varying.

Have you drained your oil yet? I would be interested to see how much oil comes out when the stick shows 7 qts. As I look at your pan compared to mine, there is simply no way that the same dipstick can be used. The volume to height ratio between our two pans would be very different. This should mean that different dipsticks are used for different pans or at least different dipstick tubes. It is possible yours has mis-matched parts that are indicating an erroneous level.

Another potential scenario would be large contamination in the pan. My pan has as similar sump inlet design and the entry slot is relatively small. Something floating on top of oil could partially block the entrance when oil gets to a certain level. This seems quite unlikely however. Further, your historical pressure chart sure looks like an air problem over a blockage problem. However, something that is variably restricting the opening could look similar. I new a guy that tore down a recently rebuilt auto engine and found a shop rag.

Larry

Hi,

I will drain oil and make measurement shortly. Also check oil screen and open oil filter to check potential metal chips,etc.

Regarding crankcase pressure, i'm using an Antisplat Aero valve connected to exhaust. breather line coming from separator is draining oil to exhaust through this valve. Exhaust positive pressure creates a slight (?) pressure inside the crankcase. This is also a clue for my root cause issue. This may be totally unrelated but i will also remove this valve for my investigations.

http://www.vansairforce.com/community/showthread.php?t=118988&highlight=asa

Cyril

orionis said:

Hi,

I got this sump :....

....IO-360-A1A has a wide shallow oil sump and the oil pickup is towards the rear....

....I also suspect half raven installation. My engine blows through breather line, so this means there is pressure in the crankcase.
And my air-oil separator has one plug at a pick-up located under the sump...

Click to expand...

I have the same sump and regularity operate below 4 qts with no oil pressure flux. The actual intake hole in the pickup is right about in the center of the sump, rather than to the rear.

I also find it curious that the oil return from the slobber pot is under the pan. How high is the actual slobber pot in relation to the oil level? Is there a check valve as in a "full" inverted system? Anyway, I think it's a good idea to cap that off and run a "normal" breather system for a while and see if the behavior changes.

Toobuilder said:

Is there a check valve as in a "full" inverted system?

Click to expand...

Great minds and all that rot....I was just off on another page to check that very question.

The in-tank ball valve is stuck in the inverted position. That means blow-by pressure builds in the case until it forces sump oil level down to the top of the Christen 810-R oil return fitting, which acts as a standpipe....and results in a very low sump oil level.

http://www.rv7factory.com/files/inverted_oil.pdf

Hi there,

So i drained oil and checked suction screen. All is OK : suction screen is clean (no chip and nothing suspicious), oil drained is 5.7 qts for 6 qts on the dip stick so all is fine.

>>The in-tank ball valve is stuck in the inverted position. That means blow-by pressure builds in the case until it forces sump oil level down to the top of the Christen 810-R oil return fitting, which acts as a standpipe....and results in a very low sump oil level.

Indeed stuck ball is an interesting idea and could be the trick. And i share this idea about excessive pressure in the crankcase that could lead to drain oil in the christen can, at least to fill the can and may be to vent it overboard.

Next time i will remove the breather line valve that is plugged on the exhaust. And make some tests.
Then, i will unplug christen oil separator. EFIS recording feature will be a good way to compare results.

i will let you know.
Thanks all for your helpful inputs

Cyril

1st thing I would do is make sure the dipstick is reading correctly and that you have the amount of oil in the engine that the dipstick says is in there. If it is accurate, then I would suspect that their is a suction leak in the internal plumbing to the oil pump inlet that is being uncovered when the oil level is lower. Might be the sump gasket between the accessory housing and sump, where the oil suction port in the sump and accessory housing is close to the edge of the gasket. If not perfectly flat on both surfaces it is easy to leak there. Have seen it before.
The standard sump pick up, is pretty far forward in the sump, pretty central location, so if you can make it happen nose down and then correct it nose up I think this would prove a suction plumbing leak in the rear of the engine where it is all located.
Good Luck,
Mahlon

... I sort of speed read this thread so I very well could have missed it, but I didn't see any mention of the increased oil temperature. My engines oil temperatures seems to increase about twelve degrees with every quart down from seven. My oil pressure drops accordingly with reduction in oil volume. The end result seems to mimic the conditions you are experiencing here. My engine oil pressures are dramatically effected by oil temperature, approximately one psi per degree of temperature in the ranges expressed by the graphs in this thread. Perhaps, this is part of the issue being researched here.Thanks, Allan...

Oil pressure with half Christen

If your oil system is set up with the christen system like it is with the full system, I would take a look at the ball in the christen slobber pot. I have seen this ball look like a coal clinker, not round/spherical at all, and leaked air into the oil system.....

PS I have been intimate with many aerobatic aircraft that had full inverted systems. They were always pristine on the inside of the engines when torn down for maintenance. From my experience I do not believe there is anything harmful happening because of the oil separator.

Hi there,

I finally found time and also nice weather to achieve tests.

So i started by disconnecting half christen (can) and connect breather outboard (RV original design for breather line). During flight, same symptoms : oil pressure fluctuation during flight. Christen oil/air separator was not the root cause.

Following tests, oil level became very low : dipstick readings showed about 4.5 qts in the io-360 A1A sump.

I decided to add oil : 3 extra qts in order to get something like 7.5-8 qts. I started engine for some minutes and went back to home.
I was really surprised, 24h later to read 6 qts on the dipstick...

May be something wrong, so i added 1 extra qt and read 7qts...

At this time, i realized that my dipstick readings was wrong below 6 qts.

Further tests showed the following correspondence :

Dipstick reading (Qts) / Real oil qty in sump (Qts)


8 / 8
7 / 7
6 / 6
5.5 / 5 (-10%)
5 / 4 (-25%) (Oil fluctuation seen on EFIS)
4.5 / 3 (-50%) (Oil fluctuation seen on EFIS)

I then asked the guy who sold me the engine. he confirmed that dipstick was genuine and fitted with 360 A1A.

In short, during my oil consumption tests, it sounds obvious that my dipstick readings was wrong below 6qts. I noticed oil fluctuation at 5 qts (4 qts in sump) and below. And my last test flight was achieved with something like 3 qts in the sump. All went fine, thanks god !

3 related points from this :

1/ A1A dipstick measurements is not reliable below 6 qts. i suspect this is linked to the "wide" shape of the sump that creates discrepancies in the readings. But i'm surprised by the huge error margin.

2/ Sump gasket leak was not the root cause. At 4 qts and below, oil pressure fluctuation is probably normal on this engine.

3/ Interestingly, tests showed that Christen/Raven "oil/air separator" are not at all efficient to recover oil in the sump. I recently added a new and dedicated oil separator that made oil consumption drop from 0.4 qt/hr to a fourth (0.1 qt/h). Obviously, Christen/Raven devices have been designed for inverted flight and are efficient for this main purpose.

Thanks all for uour input on this issue and happy new year ! Enjoy your 2015 flights !


Cyril