CHAS CAS:
I have a new Penn Yan reman which went into service on 6/9/04. After
putting 15 hours on her, I had an oil/filter change with 20/50 mineral oil (thats what the mechanic used). On 8/31/04 with 44 hours on the reman, I had an Annual resulting in compressions 80/ 1-76 2- 76 3-77 4-77. I also had another oil and filter change, this time with 100 wt mineral. I checked the oil that day, and it showed 8 qts. After flying 2 hours, it was down to seven. Now, at 52 hours, it has gotten down to 5 and a half; so I added 1.5 quarts. Is there such a thing as a delayed breakin. The engine has a funny smell to it, but I believe that is just the paint on the reman engine heating up. There are no visible leaks.
Could this be some sort of delayed break-in? I have been running 24 inches manifold pressure at 2400 rpm, flying below 3500 feet the whole time (when practical). All temperatures are within normal limits in all phases of flight. I am aware that the engine “blows off oil”. I should note I have an oil air seperator.
Does this sound like something to concern myself with? In all honesty it’s hard to read a warm engine’s dipstick with fresh oil. It’s much easier to read when cold. All input greatly appreciated.
Here is what I suggest:
1. I would notify Penn Yann (in writing) that you are concerned about continuing high oil consumption past the 50 hour point. This is simply to give them advance notice, while the engine is nearer to the overhaul date, to protect your interests if you do have to request warranty action later on. In this letter I would spell out what oil has been used, details on oil changes, dates, and hours, and added oil, and the power settings that have been used. Tell them what your plans are for continuing operation, and ask for any suggestions that they might have. These suggestions should include their projection for acceptable oil consumption on their reman engine.
2. I would stick with the mineral oil a while longer; either the 100 weight or the Phillips 20W50 mineral oil (depending on the weather where you are). Maintain the 6 quart level, and see what happens over the next 20 hours or so. I gather that your recent consumption was 2.5 quarts over 8 hours. This is representative of either very high power settings (meaning full throttle and 2,700 RPM, below 4,000 feet or so), incomplete break in, or a high-time engine. Unless they are operated at 65% power or below (where consumption is lower), most Lycoming IO360s will run in the neighborhood of 5 hours per quart at 70% power or higher. There is a Lycoming SB that spells out oil consumption limits, as well as a usage/power output curve. The allowable maximum usage for an IO360 at 75% or higher is roughly an hour per quart.
3. While you are in this regime of continuing break-in on the mineral oil, I would operate at 24″ and 2,500 RPM. If this power setting, the mineral oil, and a 6 quart sump level does not bring consumption up to at least 5 hours per quart by then, I would request warranty action.
Your air-oil separator is not significantly reducing oil consumption; it is simply helping to keep your belly clean. A tiny amount of oil makes a big mess on the belly. Most people talk about “blowing out the oil”, but that is rarely what actually happens. When the engine is operated above six quarts, it increases the oil mass being churned around in the engine as a very heavy mist. That deposits more oil on the cylinder walls, which results in more working past the rings, so more gets burned in the cylinder. Since the oil is ashless, and since higher power settings generate strong cylinder pressures and good burn temperatures, the higher oil burn rate doesn’t usually result in fouled spark plugs or other oil consumption symptoms. Those symptoms primarily tend to show up in very high-hour, completely worn-out engines, having low compressions, that are being “babied” at low power settings (in the effort to extend their life). It is fairly typical for the IO360 to maintain compressions in the 70s on all cylinders, despite high time and high internal cylinder and ring wear, and to be burning a quart every two hours at 75% power, with no apparent indications of oil-fouling on the plugs.
One added comment. High oil consumption is not always a bad thing. These are not car engines. They are air-cooled large-bore aluminum aircraft engines, with relatively wide internal clearances. There is such a thing as beneficial oil consumption. If all other indications remain positive, I would not worry about 2 hours per quart on an IO360. I can suggest a direct example. Find a plane (like a Bonanza) that has the Continental IO520 (8.5 to 1 compression), and maybe as little as 400-500 hours on the cylinders. The oil consumption will probably be 15 hours per quart or better. Compression on a 500 hour cylinder may be as low as 42/80 (and remain acceptable per Continental, barring burned or sticking valves). These cylinders often have to be repaired at as few as 500 hours. Pull the prop through by hand, and see how easily it can be pulled through the compression stroke. Now find a Lyc IO360 (8.7 to 1 compression) that has maybe 1,500 hours on the cylinders, with no repairs needed. It may be using 2 to 5 hours per quart. Compressions will likely be in the mid to high 70s/80. See how hard it is to pull the prop through the compression stroke. The Lyc will have easily twice the felt compression of the Continental, despite three or four times the cylinder hours. Do you really care if it uses much more oil, if it is preserving the useful life of the cylinders?