Unusual Oil Consumption?

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BeechSundowner

Filing Flight Plan
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I’ve got an older Beech with a Lycoming O-360 that came out of annual in early February. After picking it up, I noticed what seemed like unusually high oil consumption despite all cylinder compressions being 77–78. The oil also isn’t darkening as quickly as it used to, but I’m seeing roughly 4–5 hours per quart right after the change. However, while the consumption started high, it gradually slowed to about 10-13 hours per quart once the oil reached around 25 hours. Thoughts?
 
AV8R_87 said:
Did they put 8 quarts in it?
Usually the first quart gets dumped on the belly in the first 5-ish hours.
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They did but I changed my oil last week as well. Filled up the oil filter, and then added oil, totaling 6.25 Quarts. Noticed it down to 5.5qts after a few hours
 
Just a guess, the cyls may have taken a bit of a glaze, and it eventually got scraped back some. I bought a plane that hadn't flown in 30 years. The engine was pickled when it was put up. The first 3 flights I was using a quart every 5 hours. After maybe 12 hours on the plane, it settled down to quart per 8 hours(4 cyl).

Sticky ring can do that too. Have a look at the plugs and see if one jug is dark brown or near black. If one jug, then it had a stuck ring that didn't expand well.
 
I’ll keep that in mind. I fly about 10 hours a week so there’s not much time it sits for a while. I did add MMO to the gas incase it’s a ring issue but that didn’t do much
 
4-5 hours per quart...

Laughs with channel chrome cylinders
 
Check the crankcase breather tube for blockage. You could get lucky and get away for free.
 
On my IO-470 my dipstick tube was loose, so my oil level would apparently fluctuate wildly. It doesn’t take much to change the apparent oil level. I only noticed it when comparing the distance between the cowl and dipstick handle one day.
 
High oil consumption can come from 1 jug or all. Pulling upper plugs

and checking if piston tops are wet or “ponding” of oil is worthwhile.

verifying correct position of Breather is important also. Sticking into the

slipstream can result in syphoning similar to a spray gun.
 
Cheers Mag. I’m going to do a bit of flying tomorrow and pull the cowl after and look around. A fuel line was replaced during annual so perhaps they nudged the breather tube, or it’s getting clogged
 
Another tip off is mag drops. Oil fouled plugs will cause excessive drop.

Having to “ burn off” is not good.

The culprit can be identified with a “ cold cylinder check”.
 
Magman said:
Another tip off is mag drops. Oil fouled plugs will cause excessive drop.

Having to “ burn off” is not good.

The culprit can be identified with a “ cold cylinder check”.
Click to expand...
I’ll keep that in mind. I know my mags consistently drop 80-90rpm with 0 or 10 rpm difference between them
 
Magman said:
High oil consumption can come from 1 jug or all. Pulling upper plugs

and checking if piston tops are wet or “ponding” of oil is worthwhile.

verifying correct position of Breather is important also. Sticking into the

slipstream can result in syphoning similar to a spray gun.
Click to expand...
My understanding is the breather tube should stick below the cowl a small amount, but the “whistle stop” should be inside the cowl. If not, it will siphon.
 
I'm assuming no oil on the belly, or you wouldn't be asking the question. Stuck ring would be my guess. Losing a quart in 4 or 5 hours isn't going to damage anything, so I'd suggest just flying the stew out of it for a while and watching the consumption.

You said:
BeechSundowner said:
However, while the consumption started high, it gradually slowed to about 10-13 hours per quart once the oil reached around 25 hours.
Click to expand...
and you wouldn't see that sort of improvement if it were a problem with the placement of the breather tube, and that's a pretty big tube to get clogged short of something like a big mud dauber. 10-13 hours is pretty normal. What was your oil consumption prior to this? Did you cut open and inspect the oil filter after the most recent change?

Consumption of 5 hours/quart is pretty typical for the break-in period on a new engine until the rings become properly seated, then it improves quickly. What you've described sounds similar, so a ring problem (or maybe a little glazing) that cleared itself seems likely.
 
BeechSundowner said:
I did add MMO to the gas incase it’s a ring issue but that didn’t do much
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Without going down the abyss of whether or not MMO is snake oil or the best thing since sliced bread, adding it to your fuel will do nothing for a stuck ring.
This can work https://www.savvyaviation.com/wp-content/uploads/savvy_pdf/savvy-oil-control-ring-solvent-flush.pdf
Beyond what has already been mentioned, check that the breather hose has no low spots. It should be an upside down U. If there is a low spot, oil can puddle then be ejected out vs flowing back into the crankcase.
 
Hang 4 said:
Without going down the abyss of whether or not MMO is snake oil or the best thing since sliced bread, adding it to your fuel will do nothing for a stuck ring.
This can work https://www.savvyaviation.com/wp-content/uploads/savvy_pdf/savvy-oil-control-ring-solvent-flush.pdf
Beyond what has already been mentioned, check that the breather hose has no low spots. It should be an upside down U. If there is a low spot, oil can puddle then be ejected out vs flowing back into the crankcase.
Click to expand...
Old school A&P recommended it to me. Don’t plan on doing it anytime soon or ever again
 
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