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Low Oil Pressure at idle with cold oil

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RV-10 with stock IO540.

For the past 4 years of flying, when starting and warming up at idle (~1000 rpm) while the oil is below 100 deg, the oil pressure is usually ~100 psi.

The last 2 flights, (outside temps in 70-80) as soon as I have started it, oil pressure is in the 25-30psi range at 1000 rpm. If I add throttle to ~1200 rpm, then the oil pressure goes up to 30-35psi.

When in flight, the oil pressure is stable at ~70psi as it has always been.

Researching this, I think it might be a leaky pressure relief valve?

I am planning on changing the oil and filter, and checking the screens before next flight. Any other suggestions to check?

Is fixing a leaky pressure relief valve something that can be done reasonably easy? Should I check on it while I have the oil out of the engine?

Any advice or suggestions would be helpful as I have never done any work on the oil system before other than oil/filter changes
 
RV-10 with stock IO540.

For the past 4 years of flying, when starting and warming up at idle (~1000 rpm) while the oil is below 100 deg, the oil pressure is usually ~100 psi.

The last 2 flights, (outside temps in 70-80) as soon as I have started it, oil pressure is in the 25-30psi range at 1000 rpm. If I add throttle to ~1200 rpm, then the oil pressure goes up to 30-35psi.

When in flight, the oil pressure is stable at ~70psi as it has always been.

Researching this, I think it might be a leaky pressure relief valve?

I am planning on changing the oil and filter, and checking the screens before next flight. Any other suggestions to check?

Is fixing a leaky pressure relief valve something that can be done reasonably easy? Should I check on it while I have the oil out of the engine?

Any advice or suggestions would be helpful as I have never done any work on the oil system before other than oil/filter changes

#1 - check pressure sensor
#2 - if one is not bad, then ground the plane and proceed to check with mechanical gage.
#3 - plugged oil filter
#4 - Something else, diagnostics needed.
 
probably not the sensor, as the cruise PSI is unchanged from normal. Also not likely a plugged oil filter, as there are bypasses in place for when this happens. It will reduce flow some, but not likely as much as you describe.

The Oil pump produces as much volume as it can and the relief valve overflows any excess to keep the pressure at the designed level. At idle level RPMs, the pump is producing much less volume than cruise RPMs and therefore the relief is overflowing less there. So, when performance decreases, you typically see it at idle at first. The pump volume increases in a linear fashion with RPM, but the oil consumption (i.e. bleed off) is relatively static.

Question is, Why. It could be on the supply side - oil pump is producing less volume (problem in pump or blockage-either pre or post pump). Or it could be on the consumption side. If you developed a leak somewhere in the oil circuit, it would bleed off the excess oil volume that normally exists. Once the reduced oil volume or excess bleed off gets bad enough, the relief stops overflowing (no excess pressure exists) and you see pressures decrease accordingly. If a leak or blockage is marginal enough, the symptoms will disappear as RPMs increase and excess flow returns.

A small leak in the relief could create a pressure loss at low volume (i.e. idle), yet not show the effect at higher volumes, once the excess flow exceeds the flow caused from the blockage. As before, the reliefs overflows much more oil at higher RPMs. However, there are several other causes as well. However, checking the relief for leakage is pretty easy.

Larry
 
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For the past 4 years of flying, when starting and warming up at idle (~1000 rpm) while the oil is below 100 deg, the oil pressure is usually ~100 psi.
Before trying to solve oil pressure that is too low, does 100 psi at idle sound strange to anyone else?

While it may be lower than desired now, I would have been more shocked and surprised about that high psi at idle.

I don't know much about this, though, so I'm curious what others think.
 
I agree that 100 psi sounds high. I'm betting Larry has it right that there is a very small piece of trash under the relief valve check ball.
 
You are really at a fork in the road here and you cannot know which to take until you determine if it?s a gauge or engine problem. Buy beg or borrow a mechanical gauge and see what the actual pressure is. Then you will know if you have an engine problem or a gauge problem. Any other course is guessing.
Tim Andres
 
high oil pres

when weather is cool its not unusual to have 100psi if you have 70 hot.
Bob
 
Before trying to solve oil pressure that is too low, does 100 psi at idle sound strange to anyone else?

While it may be lower than desired now, I would have been more shocked and surprised about that high psi at idle.

I don't know much about this, though, so I'm curious what others think.

It depends a lot on what oil he is using. 100 cold idle and 70 hot cruise doesn't seem wrong for straight 40 or 50 weight on a cool day. 100/70 seems high for 20w50. I personally am MUCH more concerned about 35/70 than 100/70. The former is screaming that a problem is brewing and the latter is not, especially when it appears out of the blue. Once a bearing starts to go, it can go fast and the symptom is low oil pressure at idle. it is not something to be ignored. If the pressure degrades slowly over 100's of hours, it is just worn bearings that can be tolerated down to the idle pressure minimums specified. High readings can indicate blockage, but only if pressure meaningfully increases with RPMs. Otherwise it is a viscosity issue.

Larry
 
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You are really at a fork in the road here and you cannot know which to take until you determine if it’s a gauge or engine problem. Buy beg or borrow a mechanical gauge and see what the actual pressure is. Then you will know if you have an engine problem or a gauge problem. Any other course is guessing.
Tim Andres

If he has had 70 PSI in cruise for four years and still has 70 PSI in cruise, why would you assume the gauge is now incorrect. wondering if I missed something here.

Larry
 
First course of action

It may not be the gauge, or the sender, but it is always the first course of action to verify the gauge. Otherwise, you may damage the engine by adjusting something out of range with an erroneous indication. That's all.

Vic
 
While it might not be the GA or sending unit. I believe it would be prudent to verify such before tearing stuff apart. FWIW, being a retired mechanic for 50+ years that would be concidered proper procedure in any shop I worked at. Easy to get a mechanical GA and proper hose with a 1/8th pipe adapter at a parts store, remove the sender install the GA and compare setting while running on the ground. They will either be the same or maybe not. Give us a follow up and good luck.
 
While it might not be the GA or sending unit. I believe it would be prudent to verify such before tearing stuff apart. FWIW, being a retired mechanic for 50+ years that would be concidered proper procedure in any shop I worked at. Easy to get a mechanical GA and proper hose with a 1/8th pipe adapter at a parts store, remove the sender install the GA and compare setting while running on the ground. They will either be the same or maybe not. Give us a follow up and good luck.

Out of curiousity, can one be reasonably certain that a gauge accurately measuring oil pressure at idle would also accurately read oil pressure at a higher power setting, or do you have to compare gauges at a variety of power settings to be sure they are acccurate?
 
Thanks for all the suggestions. The 100psi when cold is when the weather is cold, and as the oil warms up the pressure did go down to 70 at idle or with power up.

Now as soon as I get it started it is in the 25-30psi, but increases to 70 as power is increased.

This change did happen from 1 flight to the next, it did not degrade slowly.

I will check with a mechanical gauge, but don't have any hopes that it is really the problem.

Hope to look into it this weekend.
 
Oil Pressure

The new limits which have been in effect for several years are 115 red line and 95 top of the green arc. I like to see high 80's in cruise, especially if any aerobatics are being done.
While verifying pressure with a mechanical gage is standard protocol, the steady 70# in cruise would indicate the gage and/or sender are not the issue.
I suspect you have a small piece of debris in the pressure relief valve. Depending n baffling this is pretty easy to check. Just behind the #3 cylinder is the pressure relief valve screwed into the case. Two different types. If you have a castle nut on the end of a threaded shaft turning the nut clockwise increased the pressure. If no nut the valve must be removed. Use a new crush gasket when reinstalling. You will probably need to remove some baffling to remove the valve
If the valve is the non adjustable type I would recommend installing three additional washers to raise the cruise pressure.
 
Out of curiousity, can one be reasonably certain that a gauge accurately measuring oil pressure at idle would also accurately read oil pressure at a higher power setting, or do you have to compare gauges at a variety of power settings to be sure they are acccurate?

The sensor simply has a diaphragm and a spring (assuming traditional sensors - transducers, like the Kavlico are a different animal). A lever tied to a rheostat is connected to the diaphragm to measure it's movement. It would be rare to have one of these types of sensors be accurate at one PSI and significantly inaccurate at another. Tests are usually conducted in the middle of the range or at the pressure typically read, though sweeping the gauge is good practice and doesn't take much time.

Larry
 
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Thanks for all the suggestions. The 100psi when cold is when the weather is cold, and as the oil warms up the pressure did go down to 70 at idle or with power up.

Now as soon as I get it started it is in the 25-30psi, but increases to 70 as power is increased.

This change did happen from 1 flight to the next, it did not degrade slowly.

I will check with a mechanical gauge, but don't have any hopes that it is really the problem.

Hope to look into it this weekend.

As I mentioned, pre-pump blockage can cause these symptoms as well. If you haven't done so in while, it would be wise to also check the screen in the sump. If you have a lot of blow by, you would be surprised how fast the little carbon checks seemingly reproduce. These can clog the screen up.

Larry
 
From what has been said before it appears that you have low pressure at low revs, but good pressure at normal revs. It happened suddenly, not over time.
So what could be the problem.
Bearings loose and letting pressure escape. Possible but in my opinion unlikely.
Pump worn and not able to provide enough flow, again unlikely to have happened so suddenly.
That leaves pressure escaping at low flow rates, but as flow increases pressure builds. So where could pressure escape? Most probable cause is something stuck under the pressure relief valve. Pull it, clean it and then see what happens.
 
From what has been said before it appears that you have low pressure at low revs, but good pressure at normal revs. It happened suddenly, not over time.
So what could be the problem.
Bearings loose and letting pressure escape. Possible but in my opinion unlikely.
Pump worn and not able to provide enough flow, again unlikely to have happened so suddenly.
That leaves pressure escaping at low flow rates, but as flow increases pressure builds. So where could pressure escape? Most probable cause is something stuck under the pressure relief valve. Pull it, clean it and then see what happens.

Plan on doing a oil/filter change this weekend, and will check the screen and the pressure relief valve at the same time. From these comments and other research something blocking the relief valve seems to be the most match the symptoms I am having.
Thanks,
 
Plan on doing a oil/filter change this weekend, and will check the screen and the pressure relief valve at the same time. From these comments and other research something blocking the relief valve seems to be the most match the symptoms I am having.
Thanks,

I hope it is that easy. If it is crude in the relief valve, you'll need to investigate how it got there. It is just downstream from the oil filter and something big enough to cause these symptoms won't pass through the filter media.

Larry
 
Follow up. Finally got out and did the oil change.
Changed oil, filter, and checked oil screen. There was only 1 small carbon piece in the filter (1mm x 1mm x 3mm).

I pulled the pressure regulator valve. When I inspected the ball, it had nothing on it, but there was one patch of the ball that had a discoloration like something had been on it. valve seat looked clean and round. Cleaned the ball and put it all back together.

Ran it and the oil pressure jumped right up to 80-90 just like it used to before the problem, then once oil warm settled in the 60psi range at idle.

So it does appear that there might have been something stuck onto the ball. I will continue to monitor it closely but I think this has solved the problem.

Thanks for the suggestions.

Oh, and for anyone worried about removing the pressure regulator valve, it was easy as removing a sparkplug, with the only hard part being catching the ball, and safety wiring it back together. (At least with my fat fingers).
 
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