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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
 
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?
 
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
 
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
 
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
 
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.
 
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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Just some thoughts:
New-to-me plane so you don?t 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, I?d 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
 
Vernatherm

okay so today i ran 6 washers behind the white spring had oil pressure at 78PSI all the way through a run up. But at takeoff the pressure slowly started trickling down to about 37 PSI calling for a return to the runway. I am really starting to suspect a vernatherm issue. The pressure never rises after start only goes down with engine warm up. And it goes substantially down after takeoff, has anyone seen what a failed Vernatherm does?
Thanks
 
okay so today i ran 6 washers behind the white spring had oil pressure at 78PSI all the way through a run up. But at takeoff the pressure slowly started trickling down to about 37 PSI calling for a return to the runway. I am really starting to suspect a vernatherm issue. The pressure never rises after start only goes down with engine warm up. And it goes substantially down after takeoff, has anyone seen what a failed Vernatherm does?
Thanks

Not that.

A vernatherm blocks an oil cooler bypass when the oil reaches (ballpark) 180F, forcing all flow to the cooler. A failed vernatherm simply allows oil to bypass the cooler, the result being warmer oil. If oil temperatures are normal, the vernatherm is not the source of a pressure problem.
 
okay so today i ran 6 washers behind the white spring had oil pressure at 78PSI all the way through a run up. But at takeoff the pressure slowly started trickling down to about 37 PSI calling for a return to the runway. I am really starting to suspect a vernatherm issue. The pressure never rises after start only goes down with engine warm up. And it goes substantially down after takeoff, has anyone seen what a failed Vernatherm does?
Thanks

Did you by chance fly it when you verified with the mechanical gauge?
 
Step 1

Step 1 verify gauge is reading actual pressure during ALL phases of flight. Sticking a mechanical gauge on it for a few minutes tells you nothing.
Why did you change the pressure relief spring?
I don't think 35 psi "ruined your engine" as someone stated.
 
Oil Pressure

The oil pressure green arc on the 0 360 Lycoming in certified Pitts is 60-90 psi. If I saw 35 psi in flight I would reduce power to minimum required and head for the nearest airport while looking for emergency landing sites. I would not fly the airplane again until a detailed engine inspection had been performed. I find it absolutely appalling that anyone would defend flying a Lycoming powered airplane with 35# oil pressure.
 
The oil pressure green arc on the 0 360 Lycoming in certified Pitts is 60-90 psi. If I saw 35 psi in flight I would reduce power to minimum required and head for the nearest airport while looking for emergency landing sites. I would not fly the airplane again until a detailed engine inspection had been performed. I find it absolutely appalling that anyone would defend flying a Lycoming powered airplane with 35# oil pressure.

I would verify that the gauge is accurate before tearing down a engine.
 
Oil Pressure

I would verify that the gauge is accurate before tearing down a engine.
For the second time: the OP stated that the pressure had been verified with a mechanical gage. I did not say anything about tearing down the engine. The starting point for this would be the Lycoming troubleshooting guidance.
 
Oil Pressure

After re reading the posts from the OP I have another idea. There are several small pipe plugs inside the engine. The oil pump has a pipe plug. I can't remember if all oil pumps have this plug or just some. For example I believe ECI and Superior and maybe Niagara Air Parts all manufacture oil pumps. If one of these plugs is missing or fell out, with cold oil the pump would be able to overcome the loss of oil thru the missing plug. As the oil warms up the ability to overcome would diminish. If this is a plug problem it is likely that someone forgot to properly torque the plug and is now in the bottom of the sump.
Another less likely scenario is a problem with the oil pump itself.
I will look at the parts book but I believe all the plugs are either external or inside the accessory case.
 
Oil Pressure

I verified in the Lycoming parts catalog that there is one 1/8 pipe plug in the oil pump housing. If this were missing it would dump oil into the accy case and then into the sump.
Inside the accy case there are three additional plugs that go into the crankcase. Two of these close the aft end of the main oil galleries, one on each crankcase half.
I have seen numerous statements that the normal oil pressure fitting location reads oil pressure direct from the pump. Examining a sump this appears to be incorrect. The oil goes from the pump to the oil screen and then to the oil pressure port.
Marvel and Scott tell us that there is 8-10 psi less pressure at the forward end of the right main oil gallery. It is reasonable to believe that there is a further drop on the way to the left gallery and the main bearings. So 37 psi at the normal oil pressure connection would be 29# at the right front gallery and still less at the left gallery and front main bearing.
The green arc on the oil pressure gage is there for a very good reason. I cannot comprehend anyone believing that 37 psi in flight is acceptable. Do you have the same belief about Vne or G Limit??
 
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