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  #1  
Old 12-06-2018, 04:52 PM
Phenomflyer237 Phenomflyer237 is offline
 
Join Date: Oct 2017
Location: Sarasota Florida
Posts: 13
Default Oil Pressure Low

Hello all , we have an o-360 Carb engine, after an oil change with the builder shortly after purchasing the plane the oil pressure dropped. At start we have 42 use to hang right at the green at 55. Then in flight it drops to 35 and the temp stays steady at 180-190 range. Here is what i have done
we did go from a tempest to a champion filter
w100 plus oil
Verified indications are correct via manual gauge.
changed oil and cleaned suction screen no debris found
changed the new oil filter and checked it for debris none found
Oil pressure relief-changed to the white spring part # LW-11713 went from 5 washers behind standard to 4 washers behind the white
initial start up oil pressure was at 70PSI,
In flight when the plane warms up the pressure decreases to 35 and stays steady.

Any ideas are welcome thanks
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  #2  
Old 12-06-2018, 05:41 PM
jrs14855 jrs14855 is offline
 
Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,149
Default Oil Pressure

Lycomings don't like low oil pressure. If the oil pressure in flight is actually 35 # you may have already damaged the engine. What is the history of the engine?
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  #3  
Old 12-06-2018, 07:01 PM
John Owen John Owen is offline
 
Join Date: May 2011
Location: Liberty, MO
Posts: 188
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What indicator do you have? My AFS indicator started showing low so I took it to my mechanic who tested it manually and got a reading of 75. I have a new sender but it has been cold so it hasn't been installed yet.

I hope that it is something similar.

John
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  #4  
Old 12-07-2018, 10:26 AM
jrs14855 jrs14855 is offline
 
Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,149
Default Oil Pressure

The OP stated that the readings were verified with a mechanical gage.
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  #5  
Old 12-07-2018, 12:51 PM
Petedfl12 Petedfl12 is offline
 
Join Date: Sep 2011
Location: Tampa FL
Posts: 40
Default low psi

part # LW-11713 went from 5 washers behind standard to 4 washers behind the white

When you remove the washers your oil psi decreases. If you add a washer the psi will increase . You can add up to 9 washers (check this number to be sure)
each washer should raise your psi by 5 . Hope this helps Good luck
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  #6  
Old 12-07-2018, 01:50 PM
Bicyclops Bicyclops is offline
 
Join Date: Oct 2012
Location: LA, California
Posts: 178
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Low oil pressure can have two basic causes:

1 Low pump output. That could be from wear in the pump or from the pressure relief valve dumping output at too low a pressure. The stronger spring and more washers might help, but if pressure continues to drop when warm I'd suspect...

2 Pressure losses in the system. The usual one is when the bearing clearances become large and oil dumps out from around the bearings faster than the pump can keep up with. An internal leak such as missing plug in an oil galley is possible but is not as likely to happen suddenly.

How many hours on the overhaul? Got any paperwork on the overhaul? What does oil analysis show? Sudden drop after oil change. Gotta wonder what kind of oil/supplements were in there before.

Ed Holyoke
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  #7  
Old 12-07-2018, 05:26 PM
Phenomflyer237 Phenomflyer237 is offline
 
Join Date: Oct 2017
Location: Sarasota Florida
Posts: 13
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with the stiffer spring i reduced washers as it should take less initially.

I have good pressure at start up75 psi then it decreases reciprocal of oil temp rise. it stabilizes at 40psi.
It never rises with increase of RPM only ever goes down from the baseline engine start.
I am still suspicious of the oil pressure relief seat although it looks okay.
I think tomo I will try another washer or two just to see if it suddenly seats..

has anyone ever checked pressure on the oil cooler side(the pilot side of the accessory case)???
I found a plug there that i removed and fitted a second oil line and fitting to i am hoping to check differential pressure and see if the issue is in the oil cooler circuit. I guess the pump could be bad or losing pressure elsewhere.
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  #8  
Old 12-07-2018, 10:45 PM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 3,339
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a thick, straight weight oil like the 50 weight W100 is going to produce a lot more pressure when cold due to it's viscosity when cold. This is normal and expected. It's too thick for winter op's in my opinion (read the recommend temp ranges in the Operators manual). If you have properly confirmed the gauge, you have some work to do. I disagree with the other poster that this has damaged your engine. However, it does need to be addressed, lest you end up with no pressure in the air some day and get a forced landing with major engine damage.

Ed covered this pretty well. 1) failing pump 2) problems with pressure relief system bleeding off too much oil (debris in the seat is somewhat common and produces these symptoms) 3) excessive downstream leakage (bad bearings, leak, etc.) 4) pump inlet blockage .

Bypasses are in place to keep blocked coolers and filters from causing this problem.

The fact that it showed up- quickly points toward problems in the pressure relief or pump inlet blockage, though all are possible and in play. Lycoming pumps have had a history of self-destructing in the past though I think the current generation are fairly reliable.

EDIT: I would also ask the builder / previous owner if it always ran at 35 PSI warm, in cruise. If this is the case and the OP instrument has been properly verified, I would be looking closely for a manufacturer defect in the pressure relief assembly, as well as confirming that the correct bearings were installed in the engine during it's overhaul. For example, if the crank was ground M003 and STD bearings were used, you would see this type of problem. In theory, you would catch this when checking main bearing clearances, but I have a hunch that this check is not routinely on lycoming rebuilds, due to the difficulty in case splitting.

Larry
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Last edited by lr172 : 12-08-2018 at 09:24 AM.
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  #9  
Old 12-07-2018, 11:59 PM
tim2542 tim2542 is offline
 
Join Date: Aug 2009
Location: Redding,Ca
Posts: 631
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Just some thoughts:
New-to-me plane so you donít really know the history, did you change oil brands or type, do you know what is has been running?

With a clean filter and screens, Iíd like to know more about how you verified the oil pressure gauge. These gauges and their sensors are far less reliable than the oil system.

Messing around with the pressure relief valve may mask a developing problem.

And finally does this plane have an inverted oil system?
Good luck
Tim Andres
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  #10  
Old 12-08-2018, 06:51 AM
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DanH DanH is offline
 
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Location: 08A
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Quote:
Originally Posted by Phenomflyer237 View Post
has anyone ever checked pressure on the oil cooler side(the pilot side of the accessory case)??? I found a plug there that i removed and fitted a second oil line and fitting to i am hoping to check differential pressure and see if the issue is in the oil cooler circuit.
http://www.vansairforce.com/communit...ad.php?t=45548
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