Engine Oil Adventures

[ajudson]

I have seen a few similar topics, but I'm still a little unsure what is applicable to my situation. I just took in my Mooney (with an IO-360-A3B6D engine) for annual inspection. Oil consumption has been on the high side since I purchased a few years ago, and I didn't record adding oil as well in the beginning as I do now, so it's hard to tell if there is a trend. Lately, I have been seeing a tad less than 3 hours per qt of oil, which is above the Lycoming minimum. This has been consistent for at least the last few oil changes. An oil sample from each change has been sent to Blackstone, and has always come back very good with encouragement to "continue doing what I'm doing." No metal that I can find in the filters.

On a recent long flight (4.5+ hrs) I was around 6 qts initially. I usually don't like to fill too much higher than that since it seems to consume it even faster, so I left it there. Unfortunately, this was probably the wrong call, because towards the end of the flight I noticed the oil pressure creeping lower. Just before I reached my destination, I was definitely in the yellow and the RPM started to climb as well. It's hard to tell what pressure exactly I was at -- maybe around 50 psi? I reduced power/rpm and uneventfully landed. This event got me a little worried about the consumption as well as the engine health. I have seen various discussion about whether or not this event necessitates a teardown -- which leads me into this annual.

The mechanic took a boroscope and identified regions in each cylinder that appear to have been from rust during an extended period of disuse in the past (before me). He thinks the rest of the engine looks normal/better than average for oil and that the increased consumption is likely from blow-by in the cylinders due to these regions. There may be some evidence of a sticking exhaust valve. He is recommending to start by pulling the cylinders and taking a look at the cams, and likely completing a top overhaul.

After some research, it seems like top overhauls are pretty unpopular from some perspectives due to the risk with field assembly and pre-loading the bolts (particularly coming from Mike Busch). The advice I am seeing is to try to identify the culprit cylinder and replace just that. But from the sounds of it, all of my cylinders have a similar problem. I dug up the old pictures from a previous boroscope 2 years ago, and they still have similar indications, so it seems like they have been operating pretty consistently with this issue already. Compressions are still doing great (high 70s) on all cylinders.

What would you do in this situation? The way I see it, there are a few options:

1. Do nothing. The cylinders have good compressions and -- aside from some previous rust indications that have been there for quite some time -- seem to function well.
2. Identify the worst one and replace just that. It seems like they all have similar patterns, so there's not really a "culprit."
3. Perform a top overhaul. New cylinders would address this and the sticking exhaust valve (if there is one), but introduce some risk in the assembly.
4. Teardown/overhaul. Is the low pressure event enough to necessitate this? In that case, maybe at the very least I need to do a top, if not complete overhaul.

Pulling off at least a few cylinders would allow the cams to be inspected in case there were any issues from low pressure, so there is some merit in that besides repairing the oil issue. But on the other hand, if the engine is running well, is this overkill just to save a few tenths of a qt of oil per hour? Are there other reasons to address this more completely?

Thanks for your insight. I have included the latest boroscope images.

[Fly Boomer]

3 hours ago, ajudson said:

What would you do in this situation?

Can't advise you regarding top overhaul, but I would not launch for a 4.5+ mission with the oil below full -- even if the engine were new.  As you point out, it will blow out some enroute, but that's way better than running the oil level dangerously low at your destination.

[Schllc]

Is your belly consistently covered with oil?  Are the bottom plugs wet when pulled?  
Before I even considered a top, I would look at intake seals, and do a ring flush. If you didn’t see elevated oil temp, and cht’s, I doubt any damage occurred. I remember reading our engines can run safely on something like two quarts. 
id recommend subscribing to savvy and send them the borescopes and information. 
they really drill down and have looked at probably millions of these photos by now. 
between ai and their expertise you’re likely to get a pretty good answer. 

[N201MKTurbo]

You can either live with the high oil consumption, or fix it. The high oil consumption is likely caused by the pitting of the barrels. So the only reasonable repair is new cylinders. The fact that it hasn’t changed much in the last few years indicates that it probably won’t going forward. Just make sure you keep enough oil in it. If you are flying a long leg, I would top off the oil before you left. BTW, your engine should run fine down to about 2 Qts. Then the oil pressure will start bouncing around because the oil pump will be sucking air. Then your prop will start surging way past red line. If this starts happening, you need to throttle way back so the prop doesn’t over speed and of course land at the nearest airport.

[Crawfish]

2 hours ago, Schllc said:

id recommend subscribing to savvy and send them the borescopes and information.

I'd double this take. 

I don't see any reason to tear an engine down due to oil consumption within parameters or even replacing the cylinders (assuming the blow by isn't causing excessive crank case pressure.) Now running low oil pressure gives me pause like it seems to have to you. 50PSI I wouldn't think would be low enough to cause spun bearings but I'd reach out to savvy for their advice. TCM engines min oil pressure is well below that number. I haven't flown behind a Lycoming in 10 years so my memory on the numbers for it are failing me. 

Here's a good video reviewing oil consumption.  

 

[Flyler]

"On a recent long flight (4.5+ hrs) I was around 6 qts initially. I usually don't like to fill too much higher than that since it seems to consume it even faster, so I left it there. Unfortunately, this was probably the wrong call, because towards the end of the flight I noticed the oil pressure creeping lower. Just before I reached my destination, I was definitely in the yellow and the RPM started to climb as well. It's hard to tell what pressure exactly I was at -- maybe around 50 psi? I reduced power/rpm and uneventfully landed. This event got me a little worried about the consumption as well as the engine health. I have seen various discussion about whether or not this event necessitates a teardown -- which leads me into this annual."

What was the oil level when you landed?

[McMooney]

how many hours on the engine?  

how much oil was left when you landed?

on long trips i try to start with about 6.5quarts  knowing i'll have to top it up when i land

 

[Bartman]

I would drain the engine oil, remove the oil screen for inspection, and remove the oil filter to inspect the filter media.  If you find something abnormal or concerning, you have information that would support #4, complete engine teardown/overhaul, and eliminate 1, 2, and 3.

If you find nothing concerning, all options remain available.

[PT20J]

High oil consumption isn't an issue unless there is something broken - it's just a nuisance. Your compressions are good, the filter is clean, the oils analysis is good, and borescope only shows some cylinder pitting. So, it's an issue of how long you want to put up with it and watching engine condition and consumption trends for any changes. The compressions can be good even with pitted cylinders because the leak down compression test is done with the piston at TDC and the rings above the damaged areas. You can do an automotive style compression test to determine the overall cylinder health, but you already have pictures, so you know what the issue is. I'd just keep the oil level at 7 qts to have more margin. The oil isn't just for lubrication; it's important for engine cooling also. And since there is a lot of blowby, I'd change the oil more often.

It is possible to have good compressions with a stuck oil ring (I had that on my airplane when I bought it). So, it wouldn't hurt to try ring flushing. Savvy has instructions on its website and some mechanics use Marvel Mystery Oil with good results instead of the brew mike suggests.

[ajudson]

Thanks for the feedback so far, I will look into these suggestions. Might be time to restart my Savvy subscription. The engine is at around 1250 hours. The oil level was still at 4 qts after landing. No unusual oil temperature reading. There's usually some level of oil on the belly, but not too bad. 

[DC_Brasil]

I would definitely reactivate the Savvy subscription. 

Unfortunately, many A&Ps are spring-loaded to suggesting removing cylinders and many, many times that's just unnecessary and makes the shop receive a large paycheck. You have to think of maintenance as a medical approach: you wouldn't want an exploratory surgery to find the source of a pain.

First and foremost,  as @PT20J explained, if the oil filter, suction screen and oil analysis are fine, high oil consumption is just a nuisance. 

Secondly, there are a few things that may elevate oil consumption. Most of them do not require a cylinder to be pulled. Those corrosion pitting on the cylinder walls do not look that bad. I have the same thing on two of my cylinder walls (my plane also had a time of disuse under the previous owner). Other than that pitting you seem to have good crosshatching. Have your mechanic tried flushing the rings?

If he suspects blow-by is the culprit of the high oil consumption, it is more often caused by rings than mild pitting on the walls.

What evidence you have regarding a valve sticking? Is the engine showing morning sickness? You can try lapping the valves in place. Have you seen lead deposits on valve stems or seat on the borescope images? If they were sticking, you'd be able to see some deposits rather clearly. 

Sorry to say, but your A&P seems to be shotgunning here. He doesn't have a diagnostic and have suggested a very invasive and labor intensive intervention. I would definitely try to find a cause than starting to attack the plane with tools. Don't get me wrong: ultimately there may exist the need for a cylinder OH, but you need to be certain of it. Also, don't fall on the "let's OH all of them just in case" trap. Only do what is actually necessary for safety of flight.

Cylinder removal is a very invasive intervention, should be done by a specialized shop (not.on the field) and you'll have the risk of maintenance-induced failures. Keep that in mind.

[EricJ]

21 hours ago, ajudson said:

Thanks for the feedback so far, I will look into these suggestions. Might be time to restart my Savvy subscription. The engine is at around 1250 hours. The oil level was still at 4 qts after landing. No unusual oil temperature reading. There's usually some level of oil on the belly, but not too bad. 

It shouldn't have dropped pressure with four quarts in the sump, unless the oil was geting very hot.

+1 to just keep running it but keep a close eye on trends, both consumption and metals.    If you're handy with a wrench and don't mind spending some quality time with your engine, get a good borescope and take a peek at the cylinders yourself from time to time.   You are allowed to do this as the owner.    This way you can start seeing what's normal or not, and get a peek at the sparkplugs at the same time.    One thing to watch when doing this is how much oil is pooling in the cylinder.    You may be able to identify a particular cylinder that is using more oil this way.   This way if it does get to where you need to change a cylinder (if oil consumption continues to get much worse), you don't have to change all of them, just the one(s) most likely to be causing trouble.

Angle valve cylinders are very difficult to get right now, so if you do have to pull a cylinder you may have to send it off for overhaul.   There's always a risk when you do that that something is past overhaul limits and you'll be grounded until you can find a replacement.

So just run it with an eye on it until it is evident that you really need to do something.

[ajudson]

Thanks guys! I talked to my A&P and he didn't push back too hard about my reluctance to pull the cylinders, which is good. They cut open the latest filter and have continued to not find any metal. I am waiting for my latest Blackstone report, but as I mentioned, the last few have not seen any new or worrisome trends.

21 hours ago, DC_Brasil said:

What evidence you have regarding a valve sticking? Is the engine showing morning sickness? You can try lapping the valves in place. Have you seen lead deposits on valve stems or seat on the borescope images? If they were sticking, you'd be able to see some deposits rather clearly. 

I'll have to ask again if the A&P saw something -- the main thing we discussed is that my engine seems to occasionally "gallop" or pop a bit as I'm doing about 1000 rpm waiting to take-off. I'm not sure if this is considered morning sickness? Anyone else have experience with this? I think I remember the term "loping" for this? The A&P was not opposed to lapping the valve in place. He said we could try ring flushing, but said he hasn't typically seen improvement from that in his experience.

2 hours ago, EricJ said:

It shouldn't have dropped pressure with four quarts in the sump, unless the oil was geting very hot.

I did not see the oil temperature exceed around 200F, but I'll admit that I was preoccupied during the approach and had already pulled the power back when the RPM started creeping up. I definitely had 4 qts after the flight, which I also thought was well above the minimum to maintain pressure (I think the min is only 2qts). Is there anything else that could result in low pressure at 4 qts that I should be worried about? Thanks for the suggestions - I will look into getting a boroscope to monitor closely.

Lastly, if we are opting for not pulling the cylinders, what do you guys think about relying on only the filter inspection to verify that there were no bad outcomes from the low pressure event? Also, is there concern with the oil samples being diluted since I am frequently adding oil?

Edited Monday at 06:09 PM by ajudson

[LANCECASPER]

29 minutes ago, ajudson said:

Thanks guys! I talked to my A&P and he didn't push back too hard about my reluctance to pull the cylinders, which is good. They cut open the latest filter and have continued to not find any metal. I am waiting for my latest Blackstone report, but as I mentioned, the last few have not seen any new or worrisome trends.

I'll have to ask again if the A&P saw something -- the main thing we discussed is that my engine seems to occasionally "gallop" or pop a bit as I'm doing about 1000 rpm waiting to take-off. I'm not sure if this is considered morning sickness? Anyone else have experience with this? I think I remember the term "loping" for this? The A&P was not opposed to lapping the valve in place. He said we could try ring flushing, but said he hasn't typically seen improvement from that in his experience.

I did not see the oil temperature exceed around 200F, but I'll admit that I was preoccupied during the approach and had already pulled the power back when the RPM started creeping up. I definitely had 4 qts after the flight, which I also thought was well above the minimum to maintain pressure (I think the min is only 2qts). Is there anything else that could result in low pressure at 4 qts that I should be worried about? Thanks for the suggestions - I will look into getting a boroscope to monitor closely.

Lastly, if we are opting for not pulling the cylinders, what do you guys think about relying on only the filter inspection to verify that there were no bad outcomes from the low pressure event? Also, is there concern with the oil samples being diluted since I am frequently adding oil?

This hardly ever gets done, but is "supposed" to be done every oil change. Since you've owned the airplane, has anyone ever pulled the suction screen in the back of your engine? Your A & P probably will not be a happy camper if you suggest this as I understand it's not fun.

You will find a lot of other posts using this search: https://mooneyspace.com/search/?&q="suction screen"&page=2&quick=1&search_and_or=or&sortby=relevancy

[PT20J]

1 hour ago, ajudson said:

Thanks guys! I talked to my A&P and he didn't push back too hard about my reluctance to pull the cylinders, which is good. They cut open the latest filter and have continued to not find any metal. I am waiting for my latest Blackstone report, but as I mentioned, the last few have not seen any new or worrisome trends.

I'll have to ask again if the A&P saw something -- the main thing we discussed is that my engine seems to occasionally "gallop" or pop a bit as I'm doing about 1000 rpm waiting to take-off. I'm not sure if this is considered morning sickness? Anyone else have experience with this? I think I remember the term "loping" for this? The A&P was not opposed to lapping the valve in place. He said we could try ring flushing, but said he hasn't typically seen improvement from that in his experience.

I did not see the oil temperature exceed around 200F, but I'll admit that I was preoccupied during the approach and had already pulled the power back when the RPM started creeping up. I definitely had 4 qts after the flight, which I also thought was well above the minimum to maintain pressure (I think the min is only 2qts). Is there anything else that could result in low pressure at 4 qts that I should be worried about? Thanks for the suggestions - I will look into getting a boroscope to monitor closely.

Lastly, if we are opting for not pulling the cylinders, what do you guys think about relying on only the filter inspection to verify that there were no bad outcomes from the low pressure event? Also, is there concern with the oil samples being diluted since I am frequently adding oil?

Morning sickness is extended rough running immediately after startup that smooths out as the engine warms. It's caused by the engine running on three cylinders because the sticking valve causes one cylinder to not produce much, if any, power.

The issue you describe at 1000 rpm doesn't sound like an exhaust valve. It might be a stuck sniffle valve which is located at the bottom of the sump and is there to drain excess fuel from the intake manifold. If it sticks, it causes an intake air leak which is noticeable at lower rpms.

Before I replaced the engine, the MSE I bought had a IO-360-A3B6D that used about 3 hrs/qt. I once ran it down to 4 qts and it did show a rise in oil temperature and a drop in pressure. It had the factory gauges, so I don't know the exact numbers, but it stayed in the green ranges.

[N201MKTurbo]

I have found if you have popping and loping at low power, it is caused by an over rich idle mixture and/or an exhaust leak. The exhaust leaks are usually of no consequence, it is the over rich mixture. Have you tried leaning while you are at low power? 

[Ragsf15e]

On 2/8/2026 at 12:16 AM, ajudson said:

I have seen a few similar topics, but I'm still a little unsure what is applicable to my situation. I just took in my Mooney (with an IO-360-A3B6D engine) for annual inspection. Oil consumption has been on the high side since I purchased a few years ago, and I didn't record adding oil as well in the beginning as I do now, so it's hard to tell if there is a trend. Lately, I have been seeing a tad less than 3 hours per qt of oil, which is above the Lycoming minimum. This has been consistent for at least the last few oil changes. An oil sample from each change has been sent to Blackstone, and has always come back very good with encouragement to "continue doing what I'm doing." No metal that I can find in the filters.

On a recent long flight (4.5+ hrs) I was around 6 qts initially. I usually don't like to fill too much higher than that since it seems to consume it even faster, so I left it there. Unfortunately, this was probably the wrong call, because towards the end of the flight I noticed the oil pressure creeping lower. Just before I reached my destination, I was definitely in the yellow and the RPM started to climb as well. It's hard to tell what pressure exactly I was at -- maybe around 50 psi? I reduced power/rpm and uneventfully landed. This event got me a little worried about the consumption as well as the engine health. I have seen various discussion about whether or not this event necessitates a teardown -- which leads me into this annual.

The mechanic took a boroscope and identified regions in each cylinder that appear to have been from rust during an extended period of disuse in the past (before me). He thinks the rest of the engine looks normal/better than average for oil and that the increased consumption is likely from blow-by in the cylinders due to these regions. There may be some evidence of a sticking exhaust valve. He is recommending to start by pulling the cylinders and taking a look at the cams, and likely completing a top overhaul.

After some research, it seems like top overhauls are pretty unpopular from some perspectives due to the risk with field assembly and pre-loading the bolts (particularly coming from Mike Busch). The advice I am seeing is to try to identify the culprit cylinder and replace just that. But from the sounds of it, all of my cylinders have a similar problem. I dug up the old pictures from a previous boroscope 2 years ago, and they still have similar indications, so it seems like they have been operating pretty consistently with this issue already. Compressions are still doing great (high 70s) on all cylinders.

What would you do in this situation? The way I see it, there are a few options:

1. Do nothing. The cylinders have good compressions and -- aside from some previous rust indications that have been there for quite some time -- seem to function well.
2. Identify the worst one and replace just that. It seems like they all have similar patterns, so there's not really a "culprit."
3. Perform a top overhaul. New cylinders would address this and the sticking exhaust valve (if there is one), but introduce some risk in the assembly.
4. Teardown/overhaul. Is the low pressure event enough to necessitate this? In that case, maybe at the very least I need to do a top, if not complete overhaul.

Pulling off at least a few cylinders would allow the cams to be inspected in case there were any issues from low pressure, so there is some merit in that besides repairing the oil issue. But on the other hand, if the engine is running well, is this overkill just to save a few tenths of a qt of oil per hour? Are there other reasons to address this more completely?

Thanks for your insight. I have included the latest boroscope images.

To be clear about the leaning at 1000rpm, pull back the mixture until the engine starts to stumble, then push it back in just enough to run smoothly.  If you increase power a little to taxi, it should stumble. You want it to be real lean when you are on the ground at low power.

as you take the runway for takeoff, of course you can go full rich. If you leaned properly on the ground, and try to add full power with the mixture back still, the engine will stumble and die.

[ajudson]

I do always keep it as lean as possible during ground operations (to the point of stumbling when increasing throttle), so I don't believe it's related to being over-rich.

[Mooney in Oz]

4 hours ago, ajudson said:

my engine seems to occasionally "gallop" or pop a bit as I'm doing about 1000 rpm waiting to take-off.

If your engine is hot after a long taxi and/or a long wait at the holding point, it is not uncommon for a fuel injected Lycoming IO360 to experience popping type sounds due to high temperature fuel vaporising in the fuel lines.

This is more common on hot days, but can also happen on cooler days if the engine has been operating on the ground long enough.

It is normal IO360 behaviour.

[Utah20Gflyer]

Personally I would add an extra quart of oil to get you to 7 quarts total and carry on.  Doing a top overhaul on an engine with good compression and making full power seems like overkill.  Things may change and the calculus may swing towards intervention,  but until then I would keep flying and buying oil.  
 

Maybe just pretend you have a radial engine and your concerns about high oil consumption will fade away.  

[hammdo]

Could try a ring flush first just to see if that helps — something Savvy suggests. I too would fill it up with oil and fly until oil use is really bad or oil/filter analysis say it’s time…

-Don

[Thedude]

4 hours ago, N201MKTurbo said:

I have found if you have popping and loping at low power, it is caused by an over rich idle mixture and/or an exhaust leak. The exhaust leaks are usually of no consequence, it is the over rich mixture. Have you tried leaning while you are at low power? 

Interesting, I get popping when at idle on the ground quite often, but I lean the engine out to the point of shutting down. I had a thread on here about my exhaust where people were asking whether I had a leak... I haven't noticed any CO issues, but maybe my exhaust has some issues to look into?

[N201MKTurbo]

Most of our exhaust systems have small leaks. At slip joints, ball joints, cylinder heads, EGT probes and such. They are not a big deal because the leakage isn’t enough to be a fire hazard and it just blows out the cowl flaps, so it shouldn’t get into the cabin. 
 

When the exhaust pulses at low RPMs it will actually cause a low pressure between pulses which can suck in a small amount of oxygen rich air. That air can mix with hot rich exhaust and combust. That is the pops you hear.

[DC_Brasil]

Few considerations for @ajudson:

1 - when you say you definitely had 4 qts after that landing: did you measure it right after landing or with a cold engine? A warm engine will have plenty of oil still scattered around the internal walls and galleries and will most likely show a lower level than a cold engine, when the oil will have had the time to flow back to the sump.

2 - mild roughness or popping at 1000 rpm: have your A&P check the fuel flow setting on the injector distributor. My fuel system was overly lean and I would constantly get an unhappy engine at 1000 rpm (it would almost always quit if it hit 950 rpm). After it was adjusted, I got a normal running 1000 rpm and better cooling at takeoff power. 

3 - valves sticking will cause a very noticeable effect when the engine is cold and it gradually disappears as engine warms. You'll be able to see lead bromide deposits on exhaust valve stems and valve seats with the borescope. Lapping the valves in place can clean much of these deposits. 

4 - Ring flushing has nothing to do with sticking valves but, since your main concern began with elevated oil consumption and possible cylinder blow-by, it could help. Sometimes a cylinder ring may get stuck in place by oil sludge (our avgas burns reaaaally dirty). Flushing the rings is a cheap and minimally invasive procedure that has the ability to free up a mildly stuck ring.

5 - as @LANCECASPER said, make sure your A&P has checked the suction screen. 

6 - what kind of engine/oil system gauges do you have? Legacy analog mooney or digital engine monitors? If you have digital data, you may benefit a lot from comparing oil pressure and temperature data from different flights. If you have analog legacy gauges, it wouldn't hurt to check the oil pressure gauge for proper operation/indication.

[Joshua Blackh4t]

In regards to the pitting and oil usage, many years ago I was at a mechanical training session and one challenge was to diagnose a small honda piston engine that was using oil and blowing noticeable blue smoke. 

The answer turned out to be a tiny pit in the cylinder wall (was a new engine with a factory defect). 

It acts as a reservoir, when the piston is at the top, it fills with oil, and when its down, it empties into the combustion chamber. 

As others have said, nothing inherently wrong with using oil except annoying.

I'm in a similar situation with 1 litre in 3 hours or so which I do want to get looked at. Personally I trust my mechanic to pull a cylinder if there is any reason to. He's been doing it all his life and never heard a bad story about it.