Undrainable oil?

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Narwhal

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O-470L with a quick drain in a C182B, 12 qt capacity, 9 qt minimum for flight. The dipstick was showing 11 qts prior to oil change. I flew the airplane for an hour then started draining oil ~30 minutes after shutdown. Drained oil for an hour and changed filter. Added 9 qts. Dipstick showed 12 qts (that's also max capacity).

This means there is about 3 qts that isn't draining, I guess. It seems like a lot.

My 5 gallon oil bucket is only about 3/4 full after 2 oil changes, which confirms only 8 quarts or so are draining.

Is that high for undrainable oil, or about normal? No oil is included in the "empty weight" since this is an ancient CAR3 airplane.

Thanks!
 
Narwhal said:
O-470L with a quick drain in a C182B, 12 qt capacity, 9 qt minimum for flight. The dipstick was showing 11 qts prior to oil change. I flew the airplane for an hour then started draining oil ~30 minutes after shutdown. Drained oil for an hour and changed filter. Added 9 qts. Dipstick showed 12 qts (that's also max capacity).

This means there is about 3 qts that isn't draining, I guess. It seems like a lot.

My 5 gallon oil bucket is only about 3/4 full after 2 oil changes, which confirms only 8 quarts or so are draining.

Is that high for undrainable oil, or about normal? No oil is included in the "empty weight" since this is an ancient CAR3 airplane.

Thanks!
Click to expand...

Too much. More likely is a wrong dipstick. An airplane that old has had plenty of chances to end up with the wrong stick. A dipstick for the same engine in a 170, for instance, will have its markings higher to allow for the shift of oil backward in the sump when in the three-point attitude, and if you have that stick you'll get errors.

And the point the oil is drained from matters. Some engines have two or more plugs where oil could be drained. Need to use the most aft plug, usually.
 
Keep in mind those sticks can be very inaccurate. You mentioned it was showing 11 at the start. It could be showing 11 but only have 8. Then you drained 8, put in 9 now it shows 12.

My two 470s are each different. They 100% have the correct stick in each by part number. I always use 10 quarts as that is her happy place and one shows 8 and the other 11.

A very wise/successful mechanic that deals with these engines regularly says that’s normal. Drain them empty, ensure she’s flat. Fill to a specified volume and note what is indicated. That’s the new values. I keep them on my phone since I have two to keep them straight.

Or it could be something else :)
 
Radar Contact said:
Drain them empty, ensure she’s flat.
Click to expand...

Ensuring it is flat, or at least ensuring that the attitude is the same for each measurement is important. One guy at the airport I'm based at chased his tail insisting he had an oil consumption problem on his 182 when his nose strut went flat. The dipstick measurement changed by several quarts, making him think there was a big problem. The oil level was restored after he inflated the strut.
 
Narwhal said:
O-470L with a quick drain in a C182B, 12 qt capacity, 9 qt minimum for flight. The dipstick was showing 11 qts prior to oil change. I flew the airplane for an hour then started draining oil ~30 minutes after shutdown. Drained oil for an hour and changed filter. Added 9 qts. Dipstick showed 12 qts (that's also max capacity).

This means there is about 3 qts that isn't draining, I guess. It seems like a lot.

My 5 gallon oil bucket is only about 3/4 full after 2 oil changes, which confirms only 8 quarts or so are draining.

Is that high for undrainable oil, or about normal? No oil is included in the "empty weight" since this is an ancient CAR3 airplane.

Thanks!
Click to expand...
Check your dip-stick part number, see if you have the correct dip-stick.
 
Also, make sure your dipstick tube/housing is fully bottomed out, and tight. Mine was loose enough to where the dipstick was not always at the same depth and I would get inconsistent readings. Bottom line- the oil quarts you counted when you put them in is how much you have in the sump & filter.
 
Radar Contact said:
Keep in mind those sticks can be very inaccurate. You mentioned it was showing 11 at the start. It could be showing 11 but only have 8. Then you drained 8, put in 9 now it shows 12.

My two 470s are each different. They 100% have the correct stick in each by part number. I always use 10 quarts as that is her happy place and one shows 8 and the other 11.

A very wise/successful mechanic that deals with these engines regularly says that’s normal. Drain them empty, ensure she’s flat. Fill to a specified volume and note what is indicated. That’s the new values. I keep them on my phone since I have two to keep them straight.

Or it could be something else :)
Click to expand...
There were different dipsticks for the same airplane with the same engine. One for the taildragger, the other for when it's on floats.
 
The dipstick housing can easily catch on the edge of the socket that is attached to the crankcase such that it will be held back about an inch or so. Be absolutely certain that the tub is all the way inside the socket tube.
 
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