Q: I had an air/oil separator installed in a 1999 Cessna 182S Lycoming last August and since then the plane belly is a lot cleaner, but my oil consumption has shot up from one quart every seven to nine hours to one quart every three hours.
The mechanic is perplexed, saying he doesn’t see any oil in the discharge duct or anywhere.
Any thoughts? Is there any danger in flying the plane?
A: I can offer some basic troubleshooting thoughts on this issue with your 1999 Cessna 182S. More information would have been a little more helpful, like the total time on the engine, but let’s go with what we have.
My guess is we have a couple of different issues going on here, so I’m going to take a stab at the most obvious and easiest to begin with.
The first thing I’d suggest is that you remove the entire air/oil separator system that was just installed last August and reinstall the original breather tube, making certain it’s properly located within the engine cowl.
Don’t worry about a little oil on the belly and make several flights that you normally would make with your aircraft. Recheck the oil consumption after, say, five hours and see what it is. Hopefully, within those few hours of flight, you’ll notice any changes that may occur.
After you’ve completed that, I’d recommend you have your maintenance facility conduct a good hot differential compression check. Since I don’t have any idea how many hours are on the engine, I’m curious to learn if there is any excess blow-by the piston rings. If you can hear excess air coming from the oil filler neck on the crankcase during this test, this may be a sign of blow-by the rings, which could explain the reason for the oil consumption you’re seeing.
By reinstalling the original breather tube, we are simply eliminating the air/oil separator, which may or may not be a contributing factor to the change in oil consumption.
One other thought would be to do a good bore-scope inspection of all cylinders.
Again, because I don’t have any history on this engine, there could be a possibility of corrosion in the cylinders, considering the aircraft is now 20 years old.
If it has experienced periods of inactivity during its lifetime, possible corrosion in the cylinders could be cause for concern. Corrosion in the cylinders normally leads to excessive ring wear, which typically shows itself with excess blow-by.
I know you’re going to ask why the oil consumption increased following the installation of the air/oil separator, and I’ll be honest and tell you I’m not sure, but let’s get back to some basic troubleshooting and see where it leads us.