Cessna 182S Excessive Oil Consumption & Compression Issues

M

markw

Filing Flight Plan
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KSQL
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Skylane
My partners and I own a Cessna 182s w/ a Lycoming IO-540-AB1A5 engine (complied w/ crankshaft AD) & 1000 hours based at KSQL - San Carlos. The oil consumption changed significantly, so we had a our local mechanic do a compression check. The results were - Completed BDC compression test. Engine Temps were up and in green, see pic. Numbers are seen as, Cylinder #-TDC/BDC. All testing completed with 80 psi into cylinder. 1-75/63, 2-76/74, 3-74/72, 4-75/64, 5-72/63, 6-76/54. The mechanic also made the following observation prior to the compression check - "I looked at it today. High oil consumption is usually caused by either cylinder wall/ring wear or excessive crank case pressure. And excessive crank case pressure is caused by cylinder wall/ring wear or a leak at the crankshaft seal, that allows air into case. I pulled the lower spark plugs, they were nice and dry, #4 (LH center), plug was a little wet, but appeared to be fuel, not oil, certainly didn't seem wet enough to suspect an issue. Did compression check, all good. There is some oil around the crack seal, that could be the culprit. In looking at the plane, it doesn't look like it's using oil, belly quite clean. And the stains on the ground, by the breather are not excessive. It's possible is being burned out the exhaust, but doesn't seem like it. Not sure what to say, nothing jumping out as obvious. If I was forced to attack something, I would say the crank seal. My questions are: How to address this issue? What shop in the Bay Area should we have look into the problem & repair? Has anyone had experience with the shop in Santa Maria that is close to the Cessna Association?
 
Quart every 2 hours - Exceeds the Lycoming consumption rates. Also the plane would go for 10 hours at 6.5 qts - the change in usage was sudden.
 
A sudden change in oil consumption wouldn't ordinarily be from piston ring/cylinder wall wear.
If it was being burned one would expect the plugs to show more evidence of fouling or oil-wet, and the exhaust pipe outlet should be quite sooty on the inside surface at that consumption rate. Valve guide wear can also be a source of excessive oil consumption

The oil has to be going somewhere, but before you start tearing down an engine might want to definitively eliminate the possibility of oil leaking by cleaning the engine and airplane carefully, fly it and then inspect everything - if it is going out the crankcase breather it usually makes quite an obvious mess along the bottom of the airplane. It doesn't take much oil leaking from anywhere to make quite a mess, especially inside the pressure cowling where it can be difficult to trace the source of the leak as the oil can be distributed quite extensively by the airflow - hence the suggestion to clean everything thoroughly first.
 
You have 4 cylinders with excessive leak down at BDC compared to TDC
You don't show the results of a wobble test which forces me to assume they are excessive
You don't have a belly covered in oil which you absolutely would if the crank seal had gone bad
Conclusion?
Time to pull cylinders for an overhaul
 
I don't see how a leaky crank seal can cause low compression.

But, I also don't see how you've ruled out a leaky valve.

I would think a borescope would set this to rest. Ring blow-by leaves a distinctive pattern of residue on the piston head, and any cylinder wall scoring should be visible.

Sudden oil and compression loss can be the result of severe detonation, or overheating.

We've taken the CAP 182T to Rossi at Palo Alto chasing excessive oil leaks. He's thorough, and not cheap.
 
If this oil consumption increase occurred after the engine was re-assembled, I'd guess some one broke a ring putting a cylinder on.
 
The 182T came out in 2001. Lycoming replaced the valve guide material with a high-chromium bronze in 1999, and the valve guide wear problem went away. I doubt that the OP has a problem there.

I'm wondering about the mechanic. An air leak INTO the case through the front seal pressurizing the case? Please.

If the oil consumption went up when the engine was disassembled for the crank AD, they probably rehoned the cylinders. Whether they put in new rings or not, the pilot has to run the engine HARD to get the rings seated. Babying it will glaze the walls and rings before they're seated and it will burn lots of oil.

If it started using oil when a new partner started flying the airplane, see if he's filling the sump right to the max. Some Lycs don't like that and they'll blow the oil overboard out the breather.
 
Thank you all for your responses. Lower plug were nice & dry with the exception of #4 LH center that was wet from fuel & not oil. We have not completed a wobble test & will bring that to our mechanic's attention. The belly does not have an abnormal amount of oil on it.
 
No new partners & we do not fill the oil above 6 - 6.5 qts.
 
Dan Thomas said:
The 182T came out in 2001. Lycoming replaced the valve guide material with a high-chromium bronze in 1999, and the valve guide wear problem went away. I doubt that the OP has a problem there.

I'm wondering about the mechanic. An air leak INTO the case through the front seal pressurizing the case? Please.

If the oil consumption went up when the engine was disassembled for the crank AD, they probably rehoned the cylinders. Whether they put in new rings or not, the pilot has to run the engine HARD to get the rings seated. Babying it will glaze the walls and rings before they're seated and it will burn lots of oil.

If it started using oil when a new partner started flying the airplane, see if he's filling the sump right to the max. Some Lycs don't like that and they'll blow the oil overboard out the breather.
Click to expand...

It can happen. About 20 years ago A Rockwell Commander drove us nuts with oil leaks. Long story short; some idiot had installed the wrong crank seal. It wasn't even touching the crank. Replaced it with the proper one and the problem went away. Never underestimate idiots.
 
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