Sudden Increase in Oil Consumption on IO-360-A3B6D

[lukejb]

My engine has burned about a quart every 6 to 7 hours for a very long time.  However in the last month of flying (5 or 6 flights) I have been having to add oil after every flight.  From what I can tell it’s going through about a quart an hour now.    It’s running great with no noticeable loss in power, oil temp and pressure seem normal.  EGT and CHT seem normal (factory gauges so only get theses treading a from cylinder 4)  Compressions seem very strong on all cylinders when I cycle the prop through.  The belly does seem like it has a little more oil on it than it has had in the past.  And there is a noticeable leak up by front two cylinders that I had not noticed with the cowl off before (but this is certainly not a quart in an hour leak).  Trying to figure out best way to troubleshoot.  My assumption is that I am getting blowby from rings in one or two cylinders but I was getting some blowby before too when it was only burning a quart every 6 to 7 hours so it seems like there may be something else going on that has accelerated the consumption so quickly.  I pulled all of the bottom spark plugs 2 were very clean and dry and two were slightly wet and a little black but not terrible.    Wanted to see what the mooneyspace opinions for troubleshooting and fixing this problem are…

[N201MKTurbo]

Every time that has happened to me there was some piston problem. Have you figured out which cylinder it is? If so, you should pull that one and fix it. Otherwise, you have a top overhaul in your future.

[lukejb]

4 minutes ago, N201MKTurbo said:

Every time that has happened to me there was some piston problem. Have you figured out which cylinder it is? If so, you should pull that one and fix it. Otherwise, you have a top overhaul in your future.

No not yet.  I was planning to borescope the cylinders to look for any signs.  I was reading a Mike bush article about how you could have broken rings I’m a cylinder and still show high compression.

 

[carusoam]

Sooner is better than later…

Some metal bits have a tendency to ruin other parts…

It can be easy to check lower spark plugs to get a hint of which cylinder may be the problem…

Check the exhaust to see if oil is draining out there…

Check the engine vent to see if oil is escaping that way…

PP thoughts only, not a mechanic…

Best regards,

-a-

[philip_g]

Have you checked the plugs? I'd expect them to the you which cylinder isn't happy. Mine did when we had broken rings 

[EricJ]

A proper leak-down compression check may be useful along with the borescope inspection.   If you're not unlucky it might point to the problem right away.

How does the inside of the exhaust pipe look?   The belly behind the breather tube?

 

[Greg Ellis]

I had this issue as well.  Not saying that this is what it is but something you could check really easy.  I started going through about 1 quart per hour as well.  Turns out that the oil lines coming out of the oil cooler had been chafing against the lower cowl and there was a small hole in one of them.  When flying and under some pressure the oil was blowing out this hole.

The thing about an oil leak, if it is a leak and not a piston issue, is that the airflow inside the cowl can take that oil and disperse it anywhere.  So you may find oil not anywhere near the actual leak.  The way I noticed mine was that after every flight I would have a drop of oil on the front tire.  Otherwise there was no oil anywhere else.

[PT20J]

I bought my plane knowing it was burning about a quart every two hours. At PPI, filter was clean, borescope good, last oil analysis normal, compressions all in mid 70s. I flew it about 30 hours and put it in for annual. It was running fine. Compression in the 50s in #4. Metal in the filter. Part of a ring in the screen. Oil control ring broke and took out part of the piston when it finally let loose.

Skip

[lukejb]

8 hours ago, PT20J said:

I bought my plane knowing it was burning about a quart every two hours. At PPI, filter was clean, borescope good, last oil analysis normal, compressions all in mid 70s. I flew it about 30 hours and put it in for annual. It was running fine. Compression in the 50s in #4. Metal in the filter. Part of a ring in the screen. Oil control ring broke and took out part of the piston when it finally let loose.

Skip

Wow!  I am wondering if a broken ring can cause enough damage to require an overhaul.  Did you have to do a major overhaul after this or were you able to just have cylinder work done?

[lukejb]

12 hours ago, Greg Ellis said:

I had this issue as well.  Not saying that this is what it is but something you could check really easy.  I started going through about 1 quart per hour as well.  Turns out that the oil lines coming out of the oil cooler had been chafing against the lower cowl and there was a small hole in one of them.  When flying and under some pressure the oil was blowing out this hole.

The thing about an oil leak, if it is a leak and not a piston issue, is that the airflow inside the cowl can take that oil and disperse it anywhere.  So you may find oil not anywhere near the actual leak.  The way I noticed mine was that after every flight I would have a drop of oil on the front tire.  Otherwise there was no oil anywhere else.

That’s interesting.  I have completely cleaned the engine from all oil and going to do some static runs next to see if I can find something without having to go fly it.  Flying it just seems like with the ram air coming in the cowl it would make it too hard to find any actual leak.

So after the leak fix what did your consumption go to?  Seems like if I had a quart an hour that was just from a leak under the cowl there would be so much more oil than what I am seeing.  There is a noticeable leak under the cowl that was not there before but it just doesn’t seem like the leak mess on engine is equal to the quart an hour I am losing.

It is making the belly black too I guess that could be from breather vent or exhaust which is what I will check next.

[DXB]

20 hours ago, lukejb said:

My engine has burned about a quart every 6 to 7 hours for a very long time.  However in the last month of flying (5 or 6 flights) I have been having to add oil after every flight.  From what I can tell it’s going through about a quart an hour now.    It’s running great with no noticeable loss in power, oil temp and pressure seem normal.  EGT and CHT seem normal (factory gauges so only get theses treading a from cylinder 4)  Compressions seem very strong on all cylinders when I cycle the prop through.  The belly does seem like it has a little more oil on it than it has had in the past.  And there is a noticeable leak up by front two cylinders that I had not noticed with the cowl off before (but this is certainly not a quart in an hour leak).  Trying to figure out best way to troubleshoot.  My assumption is that I am getting blowby from rings in one or two cylinders but I was getting some blowby before too when it was only burning a quart every 6 to 7 hours so it seems like there may be something else going on that has accelerated the consumption so quickly.  I pulled all of the bottom spark plugs 2 were very clean and dry and two were slightly wet and a little black but not terrible.    Wanted to see what the mooneyspace opinions for troubleshooting and fixing this problem are…

Lycoming guide says max allowable hourly oil consumption is .006 x BHP x 4 ÷ 7.4, which for your engine is 0.64 quarts / hour, so that grounds you unfortunately.   Hopefully low compression on a cylinder and/or deep scuff marks on the wall of a cylinder by borescope will tell you which one to pull first. 

[PT20J]

3 hours ago, lukejb said:

Wow!  I am wondering if a broken ring can cause enough damage to require an overhaul.  Did you have to do a major overhaul after this or were you able to just have cylinder work done?

When the cylinder was pulled metal was found embedded in the big end con rod bearing and the cam was spalled so I ordered a factory rebuilt A3B6.

Skip

[Guest]

10 hours ago, DXB said:

Lycoming guide says max allowable hourly oil consumption is .006 x BHP x 4 ÷ 7.4, which for your engine is 0.64 quarts / hour, so that grounds you unfortunately.   Hopefully low compression on a cylinder and/or deep scuff marks on the wall of a cylinder by borescope will tell you which one to pull first. 

I’ve always wondered if the calculation for BHP is max rated HP or cruise HP (75%) from which you calculate oil consumption.  Around one quart per hour for quick math.

Clarence

[Greg Ellis]

13 hours ago, lukejb said:

That’s interesting.  I have completely cleaned the engine from all oil and going to do some static runs next to see if I can find something without having to go fly it.  Flying it just seems like with the ram air coming in the cowl it would make it too hard to find any actual leak.

So after the leak fix what did your consumption go to?  Seems like if I had a quart an hour that was just from a leak under the cowl there would be so much more oil than what I am seeing.  There is a noticeable leak under the cowl that was not there before but it just doesn’t seem like the leak mess on engine is equal to the quart an hour I am losing.

It is making the belly black too I guess that could be from breather vent or exhaust which is what I will check next.

You would think oil would be everywhere on mine but it was not.  We had to trace the leak to the oil cooler lines and a tell tale sign of where to look was the drop of oil I would get on the front tire after every flight.  My oil consumption has now returned to what it was prior to the oil cooler line leak.  If you do have a leak and not burning off the oil from an internal problem then I would think it would show up from a static run of the engine.  A&P's do static runs after oil changes to check for leaks.

[WaynePierce]

At my last annual I had squawked unusual amount of oil being used. I was having to put in two quarts after a 4 hour flight. We checked compression and it was good, we pulled the plugs and they were clean. We pulled the oil filter and cut and inspected and found nothing out to the normal. I wasn't dripping oil on the hangar floor.

What we did find was a little blow by from the the intake tube to one cylinder and some seepage from the oil fill tube where it goes in to the engine. We replaced both those "O" rings and it seems to have solved the issue. I've only flown short distances since annual so no good test yet but after a couple  of hours total flight time the oil seems to be staying on the same spot on the dip stick. We also switched from multi weight to 100 weight.

I may have some terminology incorrect in the above but it is what I remember.

 

Edited November 18, 2021 by WaynePierce
added info

[A64Pilot]

On 11/18/2021 at 6:34 AM, M20Doc said:

I’ve always wondered if the calculation for BHP is max rated HP or cruise HP (75%) from which you calculate oil consumption.  Around one quart per hour for quick math.

Clarence

99% sure it’s the HP on the data plate

[PT20J]

On 11/18/2021 at 3:34 AM, M20Doc said:

I’ve always wondered if the calculation for BHP is max rated HP or cruise HP (75%) from which you calculate oil consumption.  Around one quart per hour for quick math.

Clarence

According to the Operator’s Manual, the formula closely matches the specs for max oil consumption at 75% power and below, but yields a lower value than the spec limit at rated power.

Skip

 

[larryb]

My very first airplane 30 years ago was an American Yankee with an O320. One day oil consumption went to 1 qt/hr. It ran fine but all cylinders had broken rings. Back then I didn’t know that you should not let the prop drive the engine. I used to do descents at idle into Truckee from 10,000 feet after crossing the mountains. I suspect it was my ignorant engine operations that caused the problem.

[WAFI]

OK, so what’s the general consensus for oil consumption on healthy IO-360, no issues? Obviously better than .50 quarts and hour at cruise. 

[N201MKTurbo]

23 minutes ago, WAFI said:

OK, so what’s the general consensus for oil consumption on healthy IO-360, no issues? Obviously better than .50 quarts and hour at cruise. 

I would say 1 QT/10 hours is a good target to shoot for.

My engine before I rebuilt it would use about 1 QT in 20 hours. since I rebuilt it (it has about 50 hours on it) has yet to use any oil. I have changed the oil 3 times so far, so it hasn't had a lot of chances to use any. I can't take any credit for the low oil consumption, Continental built the cylinders, I just slid them on.

[Ragsf15e]

2 hours ago, WAFI said:

OK, so what’s the general consensus for oil consumption on healthy IO-360, no issues? Obviously better than .50 quarts and hour at cruise. 

It can also depend on your cylinders.  If you have a recent engine, you’ll likely have steel cylinders and @N201MKTurbo advice is good, but if you have chrome cylinders (which are likely older) you’ll have more consumption just due to the way the chrome wears vs the rings.

[A64Pilot]

2 hours ago, WAFI said:

OK, so what’s the general consensus for oil consumption on healthy IO-360, no issues? Obviously better than .50 quarts and hour at cruise. 

A lot depends on oil level if I try to maintain 7 qts I’ll go through oil very quickly. If I use 6 as a max an not top off until 5 I’ll use half the oil

I had an IO-540 that burned one quart every 5 hours, it had about 1900 hours on it when I prop struck it, So I did a very meticulous overhaul, new Millieium cylinders  etc.

After a short break-in, it burned one quart every 5 hours. I’ve seen engines burn a quart every few hours and yet met new specs on tear down, and I’ve seen some that burned one every 10 that had significant wear.

I would say that oil consumption within the normal range just isn’t the smoking gun we think it is, now a sudden change is though

[EricJ]

3 hours ago, WAFI said:

OK, so what’s the general consensus for oil consumption on healthy IO-360, no issues? Obviously better than .50 quarts and hour at cruise. 

A lot of people report about 1 Qt/6 hours or so.   Mine does about 1 Qt/7 hours typically.    

[PT20J]

My 1978 IO-360-A3B6D used a consistent 4.5 hours/qt for the 700 hours I owned it. This engine had been IRANed and topped by the previous owner after a taxi prop strike. It also leaked some.

My current factory rebuilt IO-360-A3B6 gets around 12 hour/qt with about 280 hours on it. Interestingly, oil consumption improved about  3 hours/quart when I switched from AS W100 to Phillips 20W50 at about 150 hours. I always fill it to 7 qts and add a quart when it gets to 6. I tried running it lower, but it didn't make a difference. I don't think this engine has much blowby as he belly stays pretty clean.

Skip

[WAFI]

4 hours ago, PT20J said:

My 1978 IO-360-A3B6D used a consistent 4.5 hours/qt for the 700 hours I owned it. This engine had been IRANed and topped by the previous owner after a taxi prop strike. It also leaked some.

My current factory rebuilt IO-360-A3B6 gets around 12 hour/qt with about 280 hours on it. Interestingly, oil consumption improved about  3 hours/quart when I switched from AS W100 to Phillips 20W50 at about 150 hours. I always fill it to 7 qts and add a quart when it gets to 6. I tried running it lower, but it didn't make a difference. I don't think this engine has much blowby as he belly stays pretty clean.

Skip

I run Philips 20w50 in South Florida and everyone seem to think its not a good idea unless I run cam guard as well because I guess there's no additives in the Philips.