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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 |
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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 |
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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/communit...&highlight=asa Cyril |
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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. |
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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 |
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