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-   -   Oil pressure fluctuation (https://vansairforce.net/community/showthread.php?t=119647)

orionis 11-18-2014 09:05 AM

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

mahlon_r 11-18-2014 10:34 AM

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

PerfTech 11-20-2014 11:42 AM

... 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...:confused:

Boyd Birchler 12-13-2014 08:30 AM

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.

orionis 12-30-2014 11:05 AM

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


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