Q: I have 21 hours Time Since New (TSN) on my RV-14A/IO390 EXP. I have been following the break-in instructions and consistently flying at greater than 65% power (usually closer to 75%…2500 rpm and wide open throttle at or below 5,500 feet). My CHTs and oil temperatures are great: 340-360 CHT and the oil temperature never goes over 195, even in a hard climb. I am using Aeroshell 100 mineral oil.
The issue is I am still burning a quart of oil every four to five hours. Should I be concerned?
Some “experts” are telling me I probably have glazed cylinders and others say just keep on flying it hard and the consumption will drop.
Brian Barrett
A: Brian, you’ve submitted a question that is quite common regarding engine oil consumption.
First of all, I’d like to tell you that the consumption you mentioned for your engine is very good.
However, the main thing you should be looking for at this point on an engine with only 21 hours on it is when the oil consumption stabilizes. You may still be at a point that the piston rings have not yet completely seated, but I think you’re getting close.
If it were me, I’d forget the advice from the “experts” and continue to fly it the same way that you’ve been. If you really had glazed cylinders at this point, I’d expect the oil consumption to be greater than what you’re seeing.
If you refer to your Lycoming Engine Installation and Operator’s Manual for the IO-390-Series, (P/N IOM-390-C), issued January 2017, you’ll find that a maximum oil consumption quantity is published on Page 53 of Appendix A, Table A-2.
I must admit when I discovered this in the manual, I was a bit disappointed because for some unknown reason, Lycoming decided to provide the maximum oil consumption using a figure of 0.006Lb/BHP/Hr. (Previously, Lycoming would state in the Operator’s Manuals a straight forward maximum consumption on the 200 horsepower versions of the IO-360 series of .80 quarts per hour.)
Now I don’t know about you, but this certainly didn’t do much for me as far as figuring out just what that stood for in quarts per hour. Fortunately, I have a good friend who is a former Lycoming engineer who I contacted to help me out. There is an application of the fence post method that allows you to calculate the consumption rate. He was kind enough to provide the answer rather than making me suffer through doing the calculations. I wonder how he knew that I hated math all through my school years?
The end result provided the maximum allowable oil consumption. According to the calculations, it ends up being about one quart in four to five hours.
As you can see, you are well within the acceptable consumption limits and hopefully by continuing to operate the engine as you have been, this consumption may reduce a little more. Even if the consumption remains as you’ve mentioned, it’s still okay and should not be a cause for concern. Let’s just make certain the rings have completed their seating process by seeing when the oil consumption stabilizes.
After all that being said, I could have just said: You should not be concerned and keep flying it as you have been. The other thing I’d like to mention are the operating parameters you mentioned. They are all fine and what I’d be expecting, so keep on flying.
One more thing: There is so much good information available in the Lycoming Operator’s Manuals if we could only get pilots and maintenance personnel to read them. I realize that the typical answer is “I’ve been flying for 30 years, and there isn’t anything in those publications that I don’t already know,” but that might not be true. So humble yourself, and do me a favor, and read what’s made available just in case something has changed or that you may have forgotten. Let’s put an end to the rumor that “pilots don’t read nor take direction well!”
Not stated how much calendar time is in those 21 hours. How much ground time is spent before and after actual time in the air?
First run to check for oil leaks and gauge operation on ground. Maybe 10 minutes followed by shutdown and cowl off inspection. Then first flight at a big, busy airport might require a tow to the runway followed by a quick run- up and 1 hour actually at 75%
Land and check oil quantity. Then if no excessive consupmption, top fuel and oil and go for 2 or 3 hours at 75% . Land and check oil again. Five hours in one day should reduce consumption. After first in flight hours vary RPM from 2000 to 2700 RPM briefly.
If oil consumption hasn’t stabilized the oil control ring might have been installed upside down on one or even all piston.
The shop I worked for did that on one engine. After 1 HR. I landed with 2 quart remaining.
Bonjour, je suis un peu étonné quand vous supposez que la bague de commande pourrait etre monté à l’envers; lors une intervention de mécanos il doit y avoir un double controle, afin d’éviter ce genre mauvais montage.
Pour les valeurs de consommation pourquoi ne pas les donner en métric ( litre ).
Je vol dans la caraîbes avec des températures plus élevées nous consommons à peu près les mêmes valeurs
Cordialement
Translated: Hello, I am a little surprised when you assume that the control ring could be mounted upside down; during an intervention of mechanics there must be a double check, in order to avoid this kind of bad assembly. For the consumption values why not give them in metric (liter). I fly in the Caribbean with higher temperatures we consume roughly the same values Regards
When swinging wrenches for a Baltimore-based Cessna dealer in the ’70’s, we’d get quite a few new aircraft from Wichita every year. In these new aircraft, and in any reman engines we installed in other aircraft, I used Aeroshell mineral oil for a full 100 hours of operation.
Using your math, max consumption is 5.8 hrs/gal, not per quart, using 7.5 lbs weight per gallon for oil. That means 1.45 hours per quart. Sounds like a high number. I wouldn’t accept it.
Then there’s the unaddressed matter of why!
Continuing consumption due to;
Rings didn’t seat well.
Oil control rings lost tension.
Ring gaps weren’t staggered during installation.
Distorted cylinder wall.
Loose intake guides.
And the tighter the stated tolerance, the more engines the manufacturer/overhauler would be repairing under warranty.
Not to say oil consumption is neccesarily a fatal flaw, up to some point.
Humm, using the math; .. .006 x 215 Hp = 1.29 lb/ hr
Oil at 59 degF is 7.5 lb, so 7.5 / 1.29 = 5.8 hrs / qt.
But then, 75% power is 161 hp, yielding 7.76 hrs/ qt.
But the engine is running with the oil temp at 180 degF, where the oil is now 7.14 lb/ qt
so, which number is to be used; hot or cold oil ?
using 7.14 lb/ qt, and 161 Hp, it still is 7.39 hrs/ qt.
I imagine it’s the oil required to make up for the use, after the engine cools, so 7.5 lb is probably the right number to use….??
I think that should be 7.5 lb/gal not 7.5 lb/qt.
Yup.! Darn….so much for doing math in the evening.
1.45 to 1..9 hrs per qt is pretty awful oil use..