Excessive oil consumption

Continental C85-12 with 0-200 crank and pistons.
Good compression, 75+ all cylinders, no external leaks and just a few drops out of the breather during a hour flight.
558 hours on NEW Continental cylinders.
Borescope and the valves look good with lots of deposits on piston top and head.
Up to a quart of oil (Phillips 20W50) every 2 1/2 hours of flight.

I’m thinking the intake valve guides are shot and it’s sucking oil
In from the cylinder heads.
Is this something the TCM cylinders are known for?
Do you think I’m on the right track?
Thanks,
Dave

Have a look at the intake valve/stem area via induction tube adapter or ??? for excessive carbon. Are all the spark plugs carboned up or wet...same for the piston tops. Maybe there's exhaust rockers with oiler holes used on the intake valves that are providing excess oiling? Not an expert here just some suggestions.

Gary

The Grumman Traveler I owned had an O-320 (upgraded to 160 HP) and would use 1.5 quarts on a 3-hour flight. I talked to one of the Grumman Gurus about it, and he asked if the plane's belly was oily. When I said yes, he suggested I stop topping off the oil after every flight, and see if the oil consumption stabilized at some lower level in the sump. (But don't let it get below 4 qts!). I found out that engine was "happy" running with 6.5 qts of oil in the sump (8 qts was "full"). Any more, and it just spit it out onto the plane's belly. And once I dropped the "full" level to 6.5 qts, it basically stopped using oil. I would have to add only about 1 quart of oil between 50-hour oil changes.

Similar story with the Commander 114 i owned after that. The Lycoming IO-540, if filled to the "full" mark (8 qts), would toss a quart overboard during the first hour, every time.
So I started I operating it with the oil level a quart "low" on the dipstick (7 qts), and it only used a quart of oil per 20 hours.

Have you tried observing what happens after that first quart is gone? Fill the oil tank, note the level on the dipstick, fly for an hour hour, then check the level on the dipstick. Note the "drop" in oil level during that hour. Repeat that process (an hour at a time) until you get to the point where either (A) the oil consumption stops (or slows dramatically), or (B) the oil level would likely be below 1/2 capacity after the next hour (4 qts on an 8 qt sump).

If your consumption stabilizes (result "A") – congratulations! You've found your engine's "happy place" regarding oil level. Just keep it at that oil level from now on, and your oil consumption will be much lower. But if you continue until you encounter situation "B", you MAY have an actual "excessive oil consumption" issue, so it's time to consult your engine manuals, SBs, etc... It is surprising how much oil consumption can be considered "normal" (or at least "acceptable") for Lycoming / Continental engines!

Jim,
It’s definitely burning oil, no leaks and just a couple drops out the vent.
Belly and exterior engine are dry.
Dave