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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Cyril Bergeaud
RV7-A
France
Last edited by orionis : 12-30-2014 at 11:08 AM.
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