Question for Paul McBride, the General Aviation News engines expert: Paul, I’ve got an O-360 Lycoming. I put in factory new ECI Nickel cylinders within the last four years. I’ve probably got 400 hours or less on them.
When breaking in, the best I’ve ever achieved was maybe 11 or 12 hours on a quart of oil. Now I’m down to a quart every three hours. The oil gets black fast. You can hear blow-by in the dipstick.
At this point I’d like to do something. I didn’t check the ring gap when I installed the cylinders. I thought they were ready to go from ECI. Can I now hone and re-ring? What would be your recommendation?
Robert Laskin
Answer: Robert, there is no doubt that your break-in procedure was excellent and gave you great results with regard to the engine oil consumption.
It’s to be expected that over time an engine’s oil consumption will increase and I don’t think there is any way to determine when and how much that will be. There are just too many factors that come into play that may have an impact on oil consumption.
Since you’ve confirmed the fact that the oil gets black rather quickly, that may be a hint to the change in oil consumption.
Through your troubleshooting you’ve confirmed the blow-by is coming past the piston rings. This obviously is the reason the consumption has increased, but let’s look at some other possible contributing factors.
The oil turning black could be a result of fuel seeping into the oil during operation.
I assume you have a standard AC type fuel pump on the engine? On rare occasions, there have been cases where the fuel pump diaphragm has somehow gotten a pin hole in it and this allows a small quantity of fuel to then contaminate the engine oil which, in return, turns the fuel black in a short period of time.
I will say that I’ve never heard that this caused any other issues with the engine, but it’s something that will probably continue to get worse as engine operation time increases.
Now, before you jump into changing the fuel pump — unless you know something I don’t — I’d suggest you think about this: The Lycoming Operators Manual for your O-360 engine shows that the maximum oil consumption for your series of engines is .80 quarts per hour at rated power of 2,700 rpm.
At this point with your consumption at approximately one quart in three hours of operation, I’d suggest you continue to fly the aircraft and closely monitor the consumption and the color of the oil.
I will repeat what I said previously that it will probably get worse as time passes.
One last comment: I’d recommend a very close inspection of the complete air intake system, including the air box and security of the air filter, focusing on any gaps between the filter and the air box where outside contaminates could possibly be sucked in, especially at takeoff power. It could be that the blow-by is the real culprit from worn piston rings and the reason for the oil turning black and the fuel pump may have nothing to do with it.
By the way, I applaud you for being on top of subtle changes like this with your engine, and feel you’re capable of keeping your eye on this and take whatever action may be required in the future. Good job, Robert!
It sounds like you may have a intake leak somewhere, that will cause the oil to turn black right away after changing it. With the low run hours you say you have on the engine, it doesn’t sound like the rings are wiped, Is it a Mattituck o/haul ??? Black oil is also caused by exhaust leaking in to the combustion chamber, passed the compression ring, due to badly honed cylinders, that is, in stead of having choke at the top of the cylinder, it has the apposet , in other words it is bigger at the top of the cylinder instead of smaller like it should be, some engine Co.s will do this on purpose so they can o/haul your engine very soon again and rip you off for another thirty grand . We saw a lot of these engines where the cylinders were purposely bored backwards, they suck all the exhaust and debris down into the crankcase turning the oil black. the unsuspecting owner is told he needs an o/haul again, who is to say otherwise !!!
You did not say if burning a qt when putting in 8 qts? or 7? 6? Most Lycoming 360’s settle around 6 qts then burn settles in to a lesser rate. But, if you top off it may burn the first qt or 2 quickly.
Only use oil that is not 50% synthetic, since lead in the fuel and synthetic oil will cause sludge to develop over time. Camguard in the oil on every change and marvel mystery oil in the fuel will keep everything working…….Lean on the ground and in the air…..
Go with your own suggestion and get it over with, hone and re-ring. The consumption was never good. Lycoming’s allowance?….an engine that often spits out the top 2 quarts leaving 6 quarts. A 4 hour flight using .8 and hour leaves you down to 2.8. And now you need to divert in IMC to an alternate? That allowance standard also determines when they have to do warranty re-rings.
It is well worth the $15-$20 to have your oil tested every 100 hours. I volunteer for the USCG Auxiliary as a pilot. Prior to that I had never had my oil tested. It is a quick, cost effective diagnostic tool to help catch serious problems early. A/C Spruce carries them. I keep an extra around to have on hand.
If you have not been leaning the mixture aggressively , there can be lead sludge in the ring grooves, keeping the rings from scraping the oil off the cylinder walls.
For your situation, Mike Bush has recommended trying a solvent flush on the cylinders to remove the sludge build up. You can google one of his webinars on how it’s done.
It does not require any disassembly, just removing an upper spark plug to do this.