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11-16-2014, 04:04 AM
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Join Date: Nov 2014
Location: France
Posts: 8
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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.
Last edited by orionis : 12-30-2014 at 10:26 AM.
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11-16-2014, 07:24 AM
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Join Date: Dec 2008
Location: Big Sandy, WY
Posts: 2,567
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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?
__________________
Actual repeat offender.
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11-16-2014, 07:42 AM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,687
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You definately have something not right going on there, you should be able to run 3-4 qts with no change in oil pressure.
__________________
Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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11-16-2014, 08:32 AM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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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
Last edited by lr172 : 11-16-2014 at 08:42 AM.
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11-16-2014, 08:49 AM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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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.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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11-16-2014, 08:55 AM
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Join Date: Nov 2010
Location: ____
Posts: 829
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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.
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11-16-2014, 09:01 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by lr172
"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
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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. 
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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11-16-2014, 09:04 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by F1R
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.
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So, is the oil pickup (suction bell) on this model relocated?
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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11-16-2014, 09:24 AM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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Quote:
Originally Posted by BillL
So, is the oil pickup (suction bell) on this model relocated?
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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
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11-16-2014, 10:07 AM
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Join Date: Nov 2010
Location: ____
Posts: 829
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Quote:
Originally Posted by BillL
So, is the oil pickup (suction bell) on this model relocated?
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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.
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