Good compressions, but still blowing oil out the breather tube. What to do?

[Oldguy]

Spoke with my mechanic yesterday about the IO-360-A3B6D in my J. It has 1450 SMOH, good compressions (74+ on all cyls) but is still blowing oil out of the breather. While I don't mind feeding it oil every 5-6 hours, I am wondering if this is going to become something more serious at some point, and I would like to handle it on the ground and not in the air.

The engine had a main bearing problem about 300 hours into its life and essentially had a bottom end overhaul. Just before I bought it in 2013, #2 cylinder was rebuilt (~1000 SMOH) by DMAX. I think I could top it and get enough hours out of it (1000+) taking into account the bottom end repair it had done to justify (rationalize) doing the work, but I hate to go into an engine that is running well just because it is blowing out some oil. If it goes to TBO or beyond with no major problems, I would swap it out for the A3B6 engine at that time.

So my question to the collective hive mind at MS is do I top the engine, continue to feed it oil, try to identify which cylinder(s) is/are pressurizing the crankcase and replace them, or what? And how could I identify the guilty cylinders? 

I know I can talk with my mechanic about this, but he in finishing my annual, and has a Bo and a Saratoga in process as well so I want to be respectful of his time. Any recommendations or thoughts on alternatives is welcome. TIA.

[DXB]

I've been through this a couple times - usually you can figure out the problem cylinder yourself, assuming there is one, before talking to the mechanic. 

But a quart every 5-6 hours isn't bad necessarily. Was there a sudden change recently?  Does the oil turn black much faster now? Are you sure the oil is going out the breather, and there's no oily residue at the exhaust pipe instead?   Do consistently have a bottom oily plug on one cylinder?  Have you borescoped your exhaust valves?  When you borescope the valves, is the crosshatch intact on the walls of all 4 cylinders without scoring?   Is one cylinder softer than the others when you pull the prop through?  Do you get an audible hiss at the exhaust pipe on one cylinder but not the others when pulling the prop through? 

[DXB]

Also Mike Busch is more helpful on this topic than I ever will be:

https://www.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2014-02_high-oil-consumption.pdf

[Oldguy]

3 minutes ago, DXB said:

I've been through this a couple times - usually you can figure out the problem cylinder yourself, assuming there is one, before talking to the mechanic. 

But a quart every 5-6 hours isn't bad necessarily. Was there a sudden change recently? Picked up from 1 every 8 or so.  Does the oil turn black much faster now? Pretty black at 15 hours or less.Are you sure the oil is going out the breather, and there's no oily residue at the exhaust pipe instead? Nope, exhaust pipe is clean, and the breather will drip consistently after a flight.  Do consistently have a bottom oily plug on one cylinder? Nothing showed any oil at annual last week when they were pulled, cleaned, and rotated.  Have you borescoped your exhaust valves? One of the next steps. When you borescope the valves, is the crosshatch intact on the walls of all 4 cylinders without scoring? I'll check when I scope them.  Is one cylinder softer than the others when you pull the prop through? Have not noticed any of them feeling any different, but will pay closer attention this weekend when I go out. Do you get an audible hiss at the exhaust pipe on one cylinder but not the others when pulling the prop through? Have not noticed, but will check this weekend.

Thanks for the thoughts. Some good tips on starting to narrow down the problem. I appreciate it.

[Bryan]

How tight (or loose) is your oil cap. My TSIO-360 was passing some oil out the breather tube on a 500-600hr engine and realized that it was related to the tabs on my oil cap not holding it tight. No oil was coming out from the cap although one flight I did find the oil cap came completely loose (off) when I know it was secured before the flight. We carefully bent the tabs back to bring the cap snug against the gasket and filler neck and that solved all my breather tub discharge issues.

[jaylw314]

I use about a quart of oil every 8-9 hours on a motor that was 100 hours after factory rebuild, so every 5-6 hours would still be quite good if not for the fact you are suggesting there was a more rapid increase in oil use recently.

i'm guessing you keep the sump filled to the same quantity and you have not changed that recently?  I used to keep 7-8 quarts in the sump, now I try to keep 6 quarts in the sump and have had noticeably less oil out the breather.

[orionflt]

what is the oil level you normally keep it at, most 360's like to be around 6 quarts. between 6-7 they will spit it out slowly over time and between 7-8 it usually only takes 1 flight to drop a quart.

Brian

 

[lifendet]

After a fresh oil change my oil stays at 8 qt for the first 20 hrs without losing oil. After that it's kept at 6-7 qt. Anymore and I'm having to add every 8 hrs. 

[Andy95W]

The two tell-tale signs that John @Oldguy mentioned is that his oil consumption increased recently from 1 qt/8 hours to now every 5-6 hours, and that the oil is "pretty black" at 15 hours or less.  This is a fairly classic sign of blow-by of the compression ring(s).  

Unlike other cylinder problems, it is often fairly difficult to identify exactly which cylinder(s) this is occurring from.  Your #2 might be newer, but not even that means much.

Like Dev mentioned, borescoping the cylinders and doing an IRAN on the 2 worst looking ones is where I'd start, then IRAN the remaining 2 if necessary.

It's not something I'd put off to your next Annual. In the interim you're putting lots of corrosive combustion by-products into your oil.  Maybe plan on a 20-25 hour oil change and do the borescope and first 2 cylinders then?

[Oldguy]

2 hours ago, Bryan said:

How tight (or loose) is your oil cap. My TSIO-360 was passing some oil out the breather tube on a 500-600hr engine and realized that it was related to the tabs on my oil cap not holding it tight. No oil was coming out from the cap although one flight I did find the oil cap came completely loose (off) when I know it was secured before the flight. We carefully bent the tabs back to bring the cap snug against the gasket and filler neck and that solved all my breather tub discharge issues.

My Lycoming has a screw on oil filler cap, so it is always tight otherwise it lets loose and would coat the inside of my cowling.

1 hour ago, jaylw314 said:

I use about a quart of oil every 8-9 hours on a motor that was 100 hours after factory rebuild, so every 5-6 hours would still be quite good if not for the fact you are suggesting there was a more rapid increase in oil use recently.

i'm guessing you keep the sump filled to the same quantity and you have not changed that recently?  I used to keep 7-8 quarts in the sump, now I try to keep 6 quarts in the sump and have had noticeably less oil out the breather.

I put in 7 at an oil change and maintain it between 6 and 6.5 qts. When planning a 3+ hour trip, I will top it up to 7, but expect to be down around 6 when I land.

1 hour ago, orionflt said:

what is the oil level you normally keep it at, most 360's like to be around 6 quarts. between 6-7 they will spit it out slowly over time and between 7-8 it usually only takes 1 flight to drop a quart.

Brian

 

Yeah, 6 +/- a bit is my target to maintain it for local flights of less than two hours.

48 minutes ago, Andy95W said:

The two tell-tale signs that John @Oldguy mentioned is that his oil consumption increased recently from 1 qt/8 hours to now every 5-6 hours, and that the oil is "pretty black" at 15 hours or less.  This is a fairly classic sign of blow-by of the compression ring(s).  

Unlike other cylinder problems, it is often fairly difficult to identify exactly which cylinder(s) this is occurring from.  Your #2 might be newer, but not even that means much.

Like Dev mentioned, borescoping the cylinders and doing an IRAN on the 2 worst looking ones is where I'd start, then IRAN the remaining 2 if necessary.

It's not something I'd put off to your next Annual. In the interim you're putting lots of corrosive combustion by-products into your oil.  Maybe plan on a 20-25 hour oil change and do the borescope and first 2 cylinders then?

I change either based on time (3-4 months) or usage (35-45 hours) with an oil analysis at each oil change. This time, it was a 15 hour oil change at annual.

 

Thanks, everyone. Some good information here.

[DXB]

27 minutes ago, Andy95W said:

It's not something I'd put off to your next Annual. In the interim you're putting lots of corrosive combustion by-products into your oil.  Maybe plan on a 20-25 hour oil change and do the borescope and first 2 cylinders then?

As a counterpoint for amiable discussion: 

If there's an acute change in oil consumption, and increased blow-by is pushing oil out the breather and turning it black, statistically it's likely to be rings on just one cylinder that are the culprit. I am not a  fan of doing more work than necessary. If I can't figure out a likely culprit based on compressions, oily plug, borescope etc., then 5-6 hours per quart is not nuts to live with for a bit.  Maybe just keep up with the higher consumption and change the oil  more often to limit  potentially corrosive blowby effects? This situation is just going to end in unacceptably high oil consumption, not engine failure.  When it gets to blowing a quart every 2-3 hours, then you really gotta do something soon, and hopefully the bad cylinder will be much more apparent at that point.

Also I'm done with IRANing cylinders after having had to pull the same one twice in 300 hours recently to address the same dang exhaust valve.  The second time, they found a tiny crack at a spark plug hole after sandblasting, and the jug had to be tossed anyway.  Going forward, if it's coming off, it gets replaced with new - the cost delta is only ~$500 for my parallel valve O-360 at least, and I never want to come back to that cylinder again until overhaul, and I certainly don't want to hear about cracks.  

[Oldguy]

9 minutes ago, DXB said:

Also I'm done with IRANing cylinders after having had to pull the same one twice in 300 hours recently to address the same dang exhaust valve.  The second time, they found a tiny crack at a spark plug hole after sandblasting, and the jug had to be tossed anyway.  Going forward, if it's coming off, it gets replaced with new - the cost delta is only ~$500 for my parallel valve O-360 at least, and I never want to come back to that cylinder again until overhaul, and I certainly don't want to hear about cracks.  

Sort of my thoughts as well. If I pull a jug, I want to go back with a new one. What I didn't mention earlier was the cylinder DMAX O/H'ed before I bought the plane had been O/H'ed a year earlier. Even with no evidence, I tend to lean towards it being the culprit. It is my #2 and also happens to be the hottest cylinder on every flight.

[carusoam]

Great input, Dev!

Signs of blow-by

1) color... oil gets discolored quickly, dark brown to black in a few hours.

2) Smell of exhaust in the fuel... as in, when you sniff the oil on the dipstick, it smells like exhaust.

3) appearance after flying... when you check the oil level...lots of bubbles making the oil look a bit foamy....

 

Blow by can pressurize the case and push more oil over-board... case pressure can be measured by your mechanic. An ordinary type of measurement...

oil foam has a tendency to increase its volume, helping it reach the case vent...

Faulty rings and worn cylinder surfaces... can allow oil to enter the cylinder...

Things that can be done to identify A problem cylinder...

dental camera.... look for health of the cross hatchings that are supposed to be there... if they are smoothed Or deeply scratched... this is a sign....

leaking valve guides, get good pics of the valves... see a good pizza?

pulling lower plugs can also find oil that has made a mess inside a cylinder...

Oil exiting the exhaust pipe... a quick look can determine if oil has been getting out an unusual way...

Hot cylinders have a tendency to wear faster than the cooler cylinders.

A broken oil ring can be a cause for loss of oil... it will come with a messy cylinder...

Show pics... cylinder surfaces, valves, lower plugs, foamy black oil....

 

PP thoughts only, fuzzy memories... all from an ancient, well worn M20C... not a mechanic.

Best regards,

-a-

[jlunseth]

I say this every time someone reports oil on the belly and using a quart every 5 or 6 hours. It is not always the right answer but it is the one most often overlooked. Contamination can block the oil quick drain from sealing. The operating engine then blows prodigious amounts of oil out through the drain and onto the belly. You think it is your breather but it is not. I got the wonderful experience of a full blown emergency descent/dive in IMC to make an airport 20 miles away with virtually zero oil pressure. The cause was a tiny but long sliver of plastic. The fix is two things. One, have your A&P drain the oil by removing the quick drain so all the little swimmers can leave through the big hole. Two, have your mechanic install a new “kit” in your quick drain which makes old quick drains seal again. My engine went from one quart every four to five hours, to one every ten or fifteen from that alone, and then we IRANd the engine and for the last more than one thousand hours I may or may not put one quart in between oil changes. The engine is over TBO so now I pretty consistently have to put one quart in between changes every 25-35 hours.

Edited February 20, 2023 by jlunseth

[warrenehc]

I am having the same problem. 
was using a quart every 5-6 hours. This weekend used 1.5 for a 3.5 hour flight and had cleaned a spot on belly prior to flight and it was covered back up. 
 

I had a cooler than #2 cylinder in the summer. Took it in machanic could not find anything. Suspected rings lined up. I asked because I was seeing more oil than normal on the ground after a flight. Oil my have went from 1qt every 6hr to 1 every 5ish. 
 

But now this is totally different. Have not had a chance to look at the plugs.(what is the torque spec for the spark plug after inspection?)

CHT’s were normal during flight.

Also something unrelated or could be related. About every few minutes I was getting a slight drop in RPMs like a slight reve down from 2475 to 2425 and then right back up to 2475. Have not had that happen before. It was consistent during the flight. Had a head wind of about 15-20 and then a tail wind of about 15-20.

[hammdo]

I use a vacuum plug on my quick drain just for that reason. Put a new one on each year…

-Don

[Fly Boomer]

7 minutes ago, hammdo said:

I use a vacuum plug on my quick drain just for that reason. Put a new one on each year…

-Don

Were you responding to @jlunseth ?  His was the only post that mentioned quick drain.  Also, what is a "vacuum plug on my quick drain"?  I have a quick drain, but no idea what a vacuum plug is.

[hammdo]

https://www.oreillyauto.com/detail/c/dorman-autograde/hardware---fasteners/vacuum-caps---connectors/vacuum-caps/54514302ba88/dorman-autograde-rubber-vacuum-cap/dag0/47396?pos=1

 

i get the assortment first, find the size that fits the quick drain and order a set (if available) based on that size. If not, I just spend $5 for the assortment again. It basically stops the dripping and when you change the oil, you’ll see it’s collected the oil. One can periodically remove the cap and empty the vacuum plug as needed…

I’ll get a pic of it on my quick drain next time I open the panel…

-Don

[Fly Boomer]

1 hour ago, hammdo said:

https://www.oreillyauto.com/detail/c/dorman-autograde/hardware---fasteners/vacuum-caps---connectors/vacuum-caps/54514302ba88/dorman-autograde-rubber-vacuum-cap/dag0/47396?pos=1

 

i get the assortment first, find the size that fits the quick drain and order a set (if available) based on that size. If not, I just spend $5 for the assortment again. It basically stops the dripping and when you change the oil, you’ll see it’s collected the oil. One can periodically remove the cap and empty the vacuum plug as needed…

I’ll get a pic of it on my quick drain next time I open the panel…

-Don

Thanks.  I don't know if these will work, but for a few bucks you can get a lifetime supply:

https://www.mcmaster.com/vacuum-tube-caps/

[hammdo]

Rubber works well, once you know the size, you can order those. My quick drain has the hose barb so rubber it is…

One could use clear tubing and the one of those though…

-Don

[rickseeman]

You have good compression and it burns a quart in 5-6 hours. I would sleep very well at night. My guess is it will be running fine for a long time.

[Fly Boomer]

1 hour ago, hammdo said:

Rubber works well, once you know the size, you can order those. My quick drain has the hose barb so rubber it is…

One could use clear tubing and the one of those though…

-Don

Ah, that makes more sense now.  No hose barb on mine.  I'll have to see if there is anything to anchor a cap to.

[Will.iam]

8 hours ago, Fly Boomer said:

Ah, that makes more sense now.  No hose barb on mine.  I'll have to see if there is anything to anchor a cap to.

Ziptie

[jlunseth]

I am not sure what a vacuum plug would do. The problem is not material entering the quick drain from outside. The problem is material swimming around in the oil that makes its way into the quick drain. Apparently it does not take much. I still have the piece that was found blocking my drain. It was some kind of plastic, long and thin. Say a quarter inch long and a sixteenth wide. As I understand it, material passes into the quick drain entrance hole, goes down the tube, and when the mechanic twists the drain to shut it, the material is captured in the seal mechanism, keeping the mechanism partially open. When the engine runs, the sump is pressurized and that blows oil out the drain that is blocked partially open. I am not sure a cap on the drain would help with that, probably the pressure would blow the cap off. In my case it took maybe two hours of flying for the engine to blow out most of the oil. As I have said before, I recommend that every once in awhile, the quick drain should be removed and the oil allowed to drain out through the big hole to remove as much of this debris as possible. There is a kit to refurbish the quick drain seal, that kit should be used to refresh the drain every few years.

The cap would certainly be worth a try though. If it would stop the blowout, that would be a big deal.

Edited February 15, 2023 by jlunseth

[RoundTwo]

I got to the end of the thread and am disappointed to not be told what @Oldguy found to be the cause.  I know it was almost 4 years ago but I’d like to hear the conclusion.