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Low Oil Pressure

ronschreck

ronschreck

Well Known Member
I have about 20 PSI at idle and was getting about 55 PSI at cruise power and that has been decreasing, so I have grounded the airplane. I have replaced the oil pressure sender, insured that the oil line to the sender is clear and the orifice in the #4 fitting on the case is open. I have checked the vernitherm and the spring and ball are both OK. I have confirmed the pressure with a mechanical gage. I have capped off the prop governor line and the prop oil line fitting at the front of the case to isolate the prop. I have removed a line from the oil cooler and get a pretty good flow of oil when cranking the engine over with the starter. I have inspected the oil filter and it has no metal of any kind. None of the actions I have mentioned result in a normal oil pressure. I have emailed Mahlon Russell, who built my engine at Mattituck and he is out of touch until January 23rd!

Show season starts soon. I need to get back in the air. Any suggestions short of pulling the engine! Thanks in advance for any and all suggestions.
 
RE: Similar Problem Solved.....

HI

In this thread I complained of a similar problem. One of the things I did (by Americans Engine who built my engine) was go with a white spring / heavy load spring number (LW11713). It did the trick. My oil pressure is now stable in cruise at or about 70.......

This is the thread see #8

http://www.vansairforce.com/communi...0&highlight=low+oil+pressure+high+temperature

ronschreck said:
I have about 20 PSI at idle and was getting about 55 PSI at cruise power and that has been decreasing, so I have grounded the airplane. I have replaced the oil pressure sender, insured that the oil line to the sender is clear and the orifice in the #4 fitting on the case is open. I have checked the vernitherm and the spring and ball are both OK. I have confirmed the pressure with a mechanical gage. I have capped off the prop governor line and the prop oil line fitting at the front of the case to isolate the prop. I have removed a line from the oil cooler and get a pretty good flow of oil when cranking the engine over with the starter. I have inspected the oil filter and it has no metal of any kind. None of the actions I have mentioned result in a normal oil pressure. I have emailed Mahlon Russell, who built my engine at Mattituck and he is out of touch until January 23rd!

Show season starts soon. I need to get back in the air. Any suggestions short of pulling the engine! Thanks in advance for any and all suggestions.
Click to expand...
 
Smokey pull the spring out, stretch it, put it back in then see if that helps. There are a number of springs that can be used and it all depends on a number of variables such as main bearing clearances, lifters, etc. Its not uncommon to have to change it after a period of time. I personally like 90-100psi cold on takeoff. I also like to use the adjustable relief valve. Whenever I've done an overhaul I choose the spring based on main bearing clearances. If the clearances are on the larger side I go up to a stiffer spring to begin with.
 
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the problem with this theory is that it assumes it has been that way from the beginning. It hasnt.

Just started recently after 1000hrs showing 30-50psi lower. This was not a gradual thing. Just started.
 
RE: After Thought

Kahuna said:
the problem with this theory is that it assumes it has been that way from the beginning. It hasnt.

Just started recently after 1000hrs showing 30-50psi lower. This was not a gradual thing. Just started.
Click to expand...

Yea, I thought of this after I sent you my take on your situation. Hate to say it ....but maybe an oil pump problem????? I hope not
 
Kahuna said:
the problem with this theory is that it assumes it has been that way from the beginning. It hasnt.

Just started recently after 1000hrs showing 30-50psi lower. This was not a gradual thing. Just started.
Click to expand...

If there's no junk in the filter then there's nothing else it could be, except for a crack in the case somewhere, or if one of the two pipe plugs that plug the cam oil galleys on the back of the case worked out. You'd have to pull the accessory case to get to these. Maybe the oil pump housing is loose. Doubt that though.

Check the screen also. Could be something is obstructing the pickup.
 
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long term elements

Springs suffer from fatigue, it's based on cycles, and steel, especially high carbon spring steels (and springs) under constant load will fracture somewhere down the working length and partially collapse.

I suspect this spring also goes to coil bind cold, a bad thing, but I have only my engine set up to detect, and it hasn't started yet. I also have the data from my oil spring, and plan to check it at my first condition insp, or if it needs to be adjusted early in the Ph1, so I will have some real data to share.

You don't want to know how many highway safety recalls I've presided over on behalf of my company as a result of this condition. :mad: Alls good at cycle 1,000,000, but at 1,000,025, it's a different characteristic. Highly highly dependent on wire quality and secondary stress risers brought on my manufacturing, handling, corrosion, etc. It can happen even if you are way off the the critical points of the goodman. Coil springs are a necessary evil. But they are evil.

Has the oil temp remained the same with the lower pressure?

Rick 90432
 
rjcthree said:
Springs suffer from fatigue, it's based on cycles, and steel, especially high carbon spring steels (and springs) under constant load will fracture somewhere down the working length and partially collapse.

I suspect this spring also goes to coil bind cold, a bad thing, but I have only my engine set up to detect, and it hasn't started yet. I also have the data from my oil spring, and plan to check it at my first condition insp, or if it needs to be adjusted early in the Ph1, so I will have some real data to share.

You don't want to know how many highway safety recalls I've presided over on behalf of my company as a result of this condition. :mad: Alls good at cycle 1,000,000, but at 1,000,025, it's a different characteristic. Highly highly dependent on wire quality and secondary stress risers brought on my manufacturing, handling, corrosion, etc. It can happen even if you are way off the the critical points of the goodman. Coil springs are a necessary evil. But they are evil.

Has the oil temp remained the same with the lower pressure?

Rick 90432
Click to expand...

Oil temps have not changed. I have an Engine Troubleshooting Check List from ECI and they mention "leak in suction lines" and I'm not sure what that means. Seems like the only suction is from the sump pickup to the pump. Any ideas?
 
ronschreck said:
Oil temps have not changed. I have an Engine Troubleshooting Check List from ECI and they mention "leak in suction lines" and I'm not sure what that means. Seems like the only suction is from the sump pickup to the pump. Any ideas?
Click to expand...

The only way that could happen is if the sump was loose, the cap on the screen was loose, or if there is a crack or hole in the sump casting.
 
The sump gasket has a hole in it to pass oil thru the sump up into the hole in the case. If a piece of that gasket broke off on the interior side of the sump, in that area, that could cause air to be sucked in.
 
That you are not seeing metal is good. When I had low oil pressure and verified the low pressure with a mechanical gauge, I looked at the screen and found lots of metal. Had to rebuild the engine.

I may pass this on to my mechanic to see what he says. He is really good with engines.
 
flyingriki said:
Your condition is confusing (to me). You say "I have about 20 PSI at idle and was getting about 55 PSI at cruise power and that has been decreasing," but then you say "Just started recently after 1000hrs showing 30-50psi lower. " Does this mean you had 85 to 105 psi at first and it is down 30-50 now running 55 and decreasing?

I fumbled along for a couple years with lower oil pressure than I thought was good. Tried adding washers and a new spring. Finally a couple knowledgeable people pointed out that the spring valve is a pop-off adjustment for high pressure and won't do anything for low oil pressure unless it is popping off at an really unusual low pressure compared to what it is designed for.

After reading this I'm thinking they were correct and the main causes of low oil pressure (lower than acceptable - which can be pretty low) is engine wear:
Click to expand...

The onset of my low oil pressure was sudden, so I don't think engine wear is an issue, especially since I have no evidence of metal in the filter. Thanks for the checklist. I think I will remove the oil lines and check them and the oil cooler for restrictions. I'll report back.
 
Ron Lee said:
That you are not seeing metal is good. When I had low oil pressure and verified the low pressure with a mechanical gauge, I looked at the screen and found lots of metal. Had to rebuild the engine.

I may pass this on to my mechanic to see what he says. He is really good with engines.
Click to expand...

Thanks. I plan on talking to Lycoming tomorrow as well.
 
Success

Everyone I talked to kept going back to the pressure relief valve (not the vernitherm) on the top of the engine (behind #3 cylinder), so I popped it off again and put 3 washers behind the spring. Voila! Oil pressure jumped up to 60 PSI. I added 2 more washers to get it up to about 80 PSI and all is well.

I didn't sleep much last night, thinking of having to pull the engine to find a spun bearing or a missing oil galley plug or worn out oil pump, or worse!

I still don't understand why that spring suddenly lost tension (if that is the root cause) but I can't argue with the results. :D I could understand it if the pressure gradually decreased over a long period of time. I'll be mulling it over for months! Anyway, I'm airworthy again. Thanks to all of you who volunteered suggestions.
 
Ronscheck - glad you're back in the air. I thought I'd use this opportunity to continue the discussion on the oil system.

We sometimes get oil pressure causes and effects backwards. Low oil pressure is not an indication of a blockage unless the blockage is on the suction side of the the pump. Low pressure would be a result of either low pump output volume (worn pump, low oil level, or low RPM) or easier oil flow downstream of the pump (hot oil or broken hose to/from oil cooler, relief valve stuck open or seat damaged or spring broken).

The oil pumps in our Lycs put out a constant volume for each revolution and will build enough pressure to make that volume (and no more and no less) go somewhere. It can go through the gallery and bearings, through the oil cooler (or not depending on the Vernatherm), to the prop governor, and can get short circuited right back to the sump by the relief valve. In reality it goes multiple places at the same time and the flow in total through all places equals the pump output.

It is the characteristics of the system downstream that determines oil pressure. Restrictions downstream will raise pressure. Warmer oil makes the oil flow easier and pressure drops.

The relief valve acts as a regulator above it's setpoint but if downstream obstructions are bad enough or oil cold enough the valve may not be able to relieve enough oil to reduce pressure and we will see pressures above the nominal 70 psi setpoint. Once the relief valve is fully shut the pressure can continue to fall as oil temperature rises and the oil flows easier.

The higher the setpoint the more oil is forced through other flowpaths like bearings and galleries and piston skirt squirters. It's like a resistor in parallel with the engine. If you raise the resistance (relief setpoint) less will get dumped back to the sump and more will go toward the moving parts of the engine.

Here is a schematic from the Lyc publication "Trouble-shooting High Oil Temperature".

567603475_qfLWv-M.jpg
 
ronschreck said:
.............I still don't understand why that spring suddenly lost tension (if that is the root cause) but I can't argue with the results. :D I could understand it if the pressure gradually decreased over a long period of time. I'll be mulling it over for months! Anyway, I'm airworthy again. Thanks to all of you who volunteered suggestions.
Click to expand...

I'd be tempted to replace the spring with a new one, just for that reason. And a careful inspection of the seat, as well.
 
ronschreck said:
Everyone I talked to kept going back to the pressure relief valve (not the vernitherm) on the top of the engine (behind #3 cylinder), so I popped it off again and put 3 washers behind the spring. Voila! Oil pressure jumped up to 60 PSI. I added 2 more washers to get it up to about 80 PSI and all is well.

I didn't sleep much last night, thinking of having to pull the engine to find a spun bearing or a missing oil galley plug or worn out oil pump, or worse!

I still don't understand why that spring suddenly lost tension (if that is the root cause) but I can't argue with the results. :D I could understand it if the pressure gradually decreased over a long period of time. I'll be mulling it over for months! Anyway, I'm airworthy again. Thanks to all of you who volunteered suggestions.
Click to expand...

Sounds like you got lucky :D

I would go one step further now and replace the spring, if it lost that much tension all of a sudden I would expect the spring will continue to fail further.
 
oil pressure

There are several different springs for a given engine. I don't think this is in the parts book. Also a limit on how many washers. Just a word of caution to check the oil screen on the bottom of the engine. It is possible for this screen to trap metal and not have it show up in the filter.
 
Timely Post

I had a similar situation on the engine we just rebuilt and started on Nov 15th. Found that by adding two washers behind the new spring and ball, OP went from 35psi at idle to 50psi cold at 1000RPM. I will be checking in flight again next time we fly.
 
more info

may be old news , but will post to add to knowledge base. Those engines with inverted oil systems have to suck oil through 1-2 ft of external oil lines and inverted oil valve, so often have to increase relief valve setting to get adequate oil pressiure indications (restriction on suction side per above post). Possibly a leak in these suction lines would suck air instead of oil. This would be seen by an oil dribble from this leak after shutdown when gravity rather than pressure diff takes over, I suspect, unless obscured by firesleeve.
More oil pressure per Marvel article is good, but colloquially can lead to higher oil temps due to pump working harder to overcome relief valve (like air compressor heating the compressed air). Many aerobatic aircraft have to wind oil pressure back, within limits of prop to govern (pres to decrease pitch props) to help control oil temps. Hope this helps someone. I'm struggling with low oil p problem at present, more ideas from this thread to try now. thanks.
 
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