What’s causing high oil consumption?

Q: We have a 1981 Cessna 182 with the Lycoming O540 L3C5D engine, which has the Cessna-installed turbo system. Lately, we’ve been experiencing some pretty high oil consumption with quite a bit of oil on the belly.

A compression check shows high compressions with the exception of #6, which has gone from 75/80 to 60 in the last 16 months. It has gone from 64 to 60 in the last three months.

We’ve had the plane for around three years. It was using about a quart every 10 hours up until about the last six months. It is currently consuming around four quarts per hour.

Our A&P says we should put in some additive and watch it for another 25 hours. The same A&P said he detected no leakage around the values of the #6 cylinder. Another A&P suggested it’s probably a valve guide.

We wonder if we should just swap the cylinder now or keep trying to figure out what’s going on with the compression and higher oil consumption.

The engine was overhauled by Lycoming in 1997. It has been based in Denver and Utah since. It currently has around 1,350 hours on the overhaul. What do you think we should do?

Brent Florek

A: My first inclination is to suspect the main problem is the #6 cylinder from the information you provided. It would indicate to me that we have a ring problem for some reason. This is somewhat confirmed by your mention of seeing quite a bit of oil on the belly of the aircraft.

Typically if the piston rings are worn out, the result is blow-by past the rings, causing the crankcase to be pressurized. The result is oil blowing out the breather tube on the belly of the aircraft.

Since the compression checks on all of the other cylinders are good, I don’t think using any type of additive would help and may, in fact, make the situation worse.

I think you may (I hope) have made a typo when saying the oil consumption went from one quart in 10 hours to four quarts in one hour. I’d rather believe it went from one quart in 10 hours to one quart in four hours and this may have been the result of possibly excessive ring wear or a broken piston ring.

The ring wear may be a result of excessive heat at that cylinder location due to a poor engine baffle. If this were the case, I believe doing a hot differential compression may answer this question.

If there is any problem with the piston rings, we would expect to hear the air being bypassed coming out the oil filler tube when the dipstick is removed or at the breather tube exit. If the piston rings are seating properly, we would not hear any air being bypassed at those locations.

Your A&P who said there was no leakage past the valves may just have overlooked listening at the oil filler tube or at the engine breather for possible air being blown past the piston rings.

You didn’t mention if the oil and filter had been changed recently since the problem began. I would do that, and closely inspect the oil filter element and oil suction screen in the bottom of the oil sump for any signs of contamination. These findings will dictate what further action may be required.

However, at this point, my suggestion would be to remove the #6 cylinder for further investigation. Once the cylinder is removed I’m certain you will find the cause of your high oil consumption. You may, depending on what you learn, be able to repair the cylinder using new replacement parts, honing the cylinder (providing there are no score marks from any broken piston rings) and return the cylinder to service.

Since this cylinder was removed and/or a replaced, we must revert to the standard engine break-in procedure set forth in Lycoming Service Instruction 1427B or its latest revision. Since this is a turbocharged engine, you will use an ashless dispersant oil for break-in as mentioned in Lycoming Service Instruction 1014M or its latest revision.

When returning the aircraft to service I want you to be certain that all of the engine baffling is in good condition and installed in its proper location. Poor baffling or improperly installed baffles can cause serious cylinder problems, which could be the root of your problem.

Question: Was the engine baffling replaced at the time this engine was installed in the aircraft? Even if it was, we’re talking a lot of hours since then and we can’t forget that the engine baffles live in a very hostile environment, so please check them closely for proper fit.

I believe this is a starting point that will reveal exactly where the problem lies, dictating the corrective action required.