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Question for Engine Experts

terrykohler

Well Known Member
Since new, my O320-D1A has burned less than a quart of oil every 25 hours.
Somewhere at just over 1,000 hours, I switched from Aeroshell 20W50 to Exxon Elite.
In the past 50 hours (now at about 1125), I've seen oil consumption rise to about one quart every 4-5 hours. One of the manuals shows .5 quarts per hour after break-in is the maximum.
Should I be concerned? What might be the cause of this sudden rise? Suggested actions?
Thanks,
Terry, CFI
RV9A N323TP
 
Oil leaves the engine through either the breather, piston rings or valve guides if not through leaks which should be easier to spot.

So you shouldn't see a step change in oil consumption when you change brands or grades. It takes time for the effects of different oils to show up.

My first line of investigation would be a leak-down test, plug examination and borescope inspection. Maybe an oil analysis or check the paper filter element for metal.

Are you doing aerobatics? That would show as a trail from the breather.
 
Oil leaves the engine through either the breather, piston rings or valve guides if not through leaks which should be easier to spot.

So you shouldn't see a step change in oil consumption when you change brands or grades. It takes time for the effects of different oils to show up.

My first line of investigation would be a leak-down test, plug examination and borescope inspection. Maybe an oil analysis or check the paper filter element for metal.

Are you doing aerobatics? That would show as a trail from the breather.

+1

Seems improbable that a brand change can cause a significant increase in consumption, at least at the rate you are talking about. I also agree that a borescope, compression test are all in order to find the problem and I would add a valve wobble test (you're looking for excessive clearance, not the minimal clearance your looking for when testing for carbon build up) if you see the leaks in the intake or exhaust. With those rates and the rapid onset, my first guess would be a broken ring and commensurate blowby. I would start with a compression test. You can buy a tester for about $100. If that much oil is coming through a valve guide, usually exhaust, you'll see major build up of coked oil on the back side of the exhaust valve with a borescope inserted through the exhaust flange.

Have you noticed a marked increase in oil on the belly? That would point you to a blowby issue and exclude the valve issue. This would be verified by the compression test. Pull the plugs and look for wet plugs and oil pooling down by the cylinder top. Visible oil would point to a compromised ring / wall interface and a need for a hone/re-ring.

If it comes down to blowby with decent compression readings, you are ok to run it and watch the compressions more closely. 1 qt in 5 hours is not really uncommon with Lycomings. Not optimum, but not a death sentence.

Larry
 
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Thanks Guys!

Rather than just accept the consumption rate, I'm probably going to start diagnostics this weekend following your suggestions. Fingers crossed that the fix is quick (another "20 minute" aviation job) and cheap (in aviationese, meaning less than 3 zeros on the price tag.)
Terry, CFI
RV9A N323TP
 
What you did is typical of changing from a long term use of a mineral base stock to a synthetic stock. You cleaned out the inside of your engine, esp rings, of gum/oil shelac etc that was keeping it happy with the Aeroshell. And now your mid time engine is showing the wear that is typical of mineral oils, but at 2000hrs - cause thats when the gum cant keep the bore gaps filled. Used to happen all the time with auto engines, but less so these days since semi synth and full synth are the norm now - iow if you start with synth you stick with it always cause its way better lubrication and doesnt suffer from wear breakdown like mineral stock.

Bottom line with oils, is you dont change base stock type until you have a new engine to work with. Our air cooled lead engines are particularly susceptible to happy gumming. When we eventually get UL gas and can go to full synthetic, this issue will disappear...as it has in auto engines of all varieties.

From the info on Exxon Elite...."Exxon Aviation Oil Elite™ 20W-50 is a premium quality, semi-synthetic, ashless-dispersant aviation piston engine oil. It is formulated from select, highly refined mineral base oils, a polyalphaolefin synthetic base oil, and ashless performance additives providing outstanding engine cleanliness, wear protection, and corrosion protection. "

Note "outstanding engine cleanliness".

So now you got what you got. Fly it and monitor. No its not a bad engine, but your new oil burn will remain the same now. You can stay with the Exxon or go back to Aeroshell if you want as youve done the cleaning and it wont much matter wrt to oil burn......wrt to other wear, ie cam wear, lifters, exhaust valves, who knows.

Just my .02 tho.
 
I agree it needs a borescope and leakdown test, time for a wobble test also. A real possibility you just have an engine problem, perhaps a broken ring or worn guide, probably nothing to do with the oil.
Tim Andres
 
If it helps, I switched from single grade to semi synthetic (aeroshell)in my 0-320-E2G at +\- 2000 hours. Oil usage was always minimal and remained that way after the switch.
 
You cleaned out the inside of your engine, esp rings, of gum/oil shelac etc that was keeping it happy with the Aeroshell.

This is what a Shell rep told me would happen when I switched from straight mineral to detergent oil in my old Stinson-----20 some years ago.

He also said the consumption would go down as the parts wore in a bit with the gunk cleaned out.

He was right on both counts.

Perhaps you will see an improvement in oil consumption???
 
There are folks on here with a lot more oil and engine smarts than me but here is what I would do. I would first look and see if one of the exhaust pipes looks like it is burning dirty. If so I would pulls a plug from each of the 2 cylinders on that header and see if they give you any info on where to look next. Another thing to look at is the crankcase vent. If it is venting into the exhaust stream the oil may be coming out there and being dissipated without you seeing it. If you cannot find anything wrong maybe one of your hangermate/friends may be messing with you. Those engines are pretty bullet proof. Good luck and let us know what you find.
 
What you did is typical of changing from a long term use of a mineral base stock to a synthetic stock. You cleaned out the inside of your engine, esp rings, of gum/oil shelac etc that was keeping it happy with the Aeroshell.

Sorry, but detergents don't work that way. There is a reason that Lycoming has you ream the valve guides when the build up gets bad enough for the valves to stick. If detergents were enough to clear it, that would be their recommendation.

Detergents can help keep an engine clean by reducing build ups and remove certain, but limited, types of build up, like sludge. But they DO NOT clean out or remove the tough struff like coked oil and carbon deposits that create havoc for the ring and valve guide areas. Only the seriously nasty chemicals do that. One other potential problem the OP is experiencing is "stuck rings" due to the ring siezing in the ring land from carbon/coked oil build up. This reduces compression and increases blowby. IF that is what happened, it is likely the new oil took the problem over the provierbial hump by creating new build ups. Some have success with MMO and other treatments to free the rings, but most are solvent based chemicals and not detergents.

Larry
 
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I never realized that cleaning coked oil and carbon out of the ring lands was as easy as simply changing to a semi-synthetic oil with Detergents.
Sarchasm aside, detergents can help keep an engine clean by reducing build ups and remove certain, but limited, types of build up, like sludge. But they DO NOT clean out or remove the tough struff like coked oil and carbon deposits that create havoc for the ring and valve guide areas.


While we are at it, Im not sure why folks routinely refer to 'detergents' in oil. I assume you must mean the ashless dispersant additive?

From the Phillips Technical Glossary available at

https://en.phillips66aviation.eu/pagina/24921/technical-glossary

"Detergent: A cleanliness additive made of metallic compounds to protect from sludge and varnish build-ups. Detergents are not allowed in aviation piston engine oils qualified under SAE J-1899 (obsolete MIL-L-22851) or SAE J-1966 (obsolete MIL-L-6082). No current aviation engine oil meeting the SAE J-1899 specification contains detergent compounds."

"Ashless Dispersant (AD):
A cleanliness additive for engine oils and widely used in aviation piston engines. Ashless dispersants do not contain metallic compounds and have no adverse affect on the break-in process."

Erich
 
While we are at it, Im not sure why folks routinely refer to 'detergents' in oil. I assume you must mean the ashless dispersant additive?

From the Phillips Technical Glossary available at

https://en.phillips66aviation.eu/pagina/24921/technical-glossary

"Detergent: A cleanliness additive made of metallic compounds to protect from sludge and varnish build-ups. Detergents are not allowed in aviation piston engine oils qualified under SAE J-1899 (obsolete MIL-L-22851) or SAE J-1966 (obsolete MIL-L-6082). No current aviation engine oil meeting the SAE J-1899 specification contains detergent compounds."

"Ashless Dispersant (AD):
A cleanliness additive for engine oils and widely used in aviation piston engines. Ashless dispersants do not contain metallic compounds and have no adverse affect on the break-in process."

Erich

This was my understanding. AD is not a detergent. Its job is to keep particles in suspension. It's path to cleanliness is by keeping the bad stuff in suspension and not letting it form on parts or fall out and create sludge. The auto industry has been using detergent oils for years, in addition to dispersants, and it's primary role is to clean up or break up sludge build ups. It is a classic surfacant. However, sludge is not the nasty villan that causes the type of things we are discussing here. It is also not really an issue in the aviation world, due to the frequency of recommended oil changes. Sludge build up usually appears with MUCH longer drain intervals than we see in aviation.

Larry
 
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If you cannot find anything wrong maybe one of your hangermate/friends may be messing with you. Those engines are pretty bullet proof. Good luck and let us know what you find.

Removing oil? That?s a seriously bad idea of a practical joke!
Tim Andres
Cozy MKIV....sold after 400 hrs
Looking and lurking.
 
This was my understanding. AD is not a detergent.

I am well aware that AD is not a detergent; that is what my previous post clarified. What people dont seem to understand is that aviation oils do not contain detergents.

Enough thread drift

Erich
 
Happy Ending

Turns out the engine wasn't burning oil or blowing it out of the stacks. Problem was traced to a failed gasket on the plate of the rear accessory cover. Puzzled as to why this would show up after over 1100 hours and never being touched, but the fix and cost could have been much worse.

While we were at it, the compression was checked (good) plugs cleaned and gapped, ignition system inspected, and overall assessment completed. Only thing remaining is to clean and replace the air filter and possibly replace one EGT probe. The engine portion of my condition inspection is them complete.

Thanks for the many thoughtful replies to my call for help. Lots of knowledge on this forum and always an opportunity to learn something new.

Terry, CFI
RV9A N323TP
 
A quart in 4 or 5 hrs from a gasket leak? Wow, that is a big leak!

And a lot of folks wasted a lot of time because you couldn't take the time to remove the cowls and look around for the obvious before posting about your "problem".
Maybe your time is more valuable than everyone elses?
 
Turns out the engine wasn't burning oil or blowing it out of the stacks. Problem was traced to a failed gasket on the plate of the rear accessory cover.

I had a similar issue with the plate just below the right mag------turns out the nut at the bottom of the mag is really easy to miss, and the nut on the block off plate is just sitting there waiting for a chance to trick some poor soul into thinking they have just loosened the mag hold down.........
 
THAT you can attribute to the synthetic oil. This is a problem as old as synthetic oil. An engine that has been run on traditional oil stocks for a long period of time (more of an age issue than run time issue) should NEVER convert to synthetic. The occurrence of gasket and seal leaks after the change is VERY common due to gasket/seal shrinkage. The older the engine, the greater the risk.

I would have mentioned this, but assumed that you ruled out a leak. Pretty hard to miss the oil staining from this volume of leak.

Larry
 
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