I have a 1973 C-172M with original the O-320 E2D, 1,698 TT airframe and engine. It’s spewing oil like crazy. I originally thought it was soot, but the surface of my underbelly has what appears to be a thick, clumpy black film on it. It’s so bad it’s creeping up the sides of the fuselage aft of the landing gear and is even on the bottom surface of the tail. I know it’s definitely oil, and I think it’s coming right out of the exhaust pipe. The oil consumption rates vary from about 1.5 quarts per hour on shorter flights with a lot of touch-n-gos to about 1 quart every two hours on long cross country flights.

About 300 hours ago, previous owner re-did the rings in two cylinders. Other than that, no majors modifications have been made except the PowerFlow exhaust roughly 150 hours ago. Both the top and bottom are the original blue Lycoming engine from 1973.

In the last 20 hours I just switch to Aeroshell 15W50 from Aeroshell 100W. I have been reading up on oils and suspect that I the switch could have something to do with this. I have also considered it could be a cracked cylinder or it may possibly have a stuck exhaust valve. Although a compression test done today shows noting obvious, I don’t know what else could be happening and I’d like to get ideas.

My mechanic is suggesting that it’s time to replace the whole engine since it’s over 12 years old, even though it is 300 hours under the 2,000 TBO. He says there’s no way to replace all four cylinders because in an engine this old, the cam is probably no good due to wear and tear. Also he claims that rebuilt cylinders aren’t an option because they will be all used up in about a year – something I have never heard.

I had hoped to take it out to at least 2,200 hours and then do at least a major overhaul. It’s obvious I will need a second opinion, but I wanted to see if anyone can help me clue into what my problem is.

I have a 68 172 with the 0320-E2D. At 1300 hrs, it was using a quart every 3-4 hrs. (I also have a Powerflow exhaust..love it!) We had good compression all around and no external leaks. We pulled the cylinders and found a cracked oil ring on #3. Replaced the cylinders with Superior millenium and I now go 25 hrs between oil changes with no oil added! I have 250 hrs since the cylinder swap.
I have always used Aeroshell 15-50 and always will. I don't believe the oil type has anything to do with these kinds of problems. The multivis oil is way better for cold starts and Aeroshell has the cam antiwear additives that Lycoming recommends. I don't think the straight weight oils do. The change may have dissolved gum or coke on the rings but the oil won't make them worse than they already were.
The consumption you are seeing points to mechanical problems. As far as the complete rebuild..once you have the cylinders off it is easy to look in the holes and inspect all cam lobes. You may be fine with the top overhaul if no other leaks,etc. 0320-E2D's are very durable and many go well past TBO especially with new jugs.
As far as overhauled cylinders go, I don't think the price difference would convince me to pass on the new ones with a warranty, considering the labor cost involved.
Check with Walter Atkinson from Advanced Power Systems(?) He is an awesome motor guru who used to be on this site. I suspect he would concur with me on these comments. He'll give you the straight scoop on oils and breakin, etc. (I hope I have the company name right. Check the archives on this site.) Good luck with your outcome! Steve