What I am finding is that by keeping the oil level between 8 and 9, I am using up half as much oil compared to if I was keeping it between 9 and 10.
Engine: IO540-C4D5D.
This is a very long story with the Cirrus. Hundered of threads on that on COPA. First of all, the IO-550N has a very a very small oil capacity for its engine size (8 quarts). Second is that on most SR22s, anything above about 6 quarts (indication per the dipstick) gets thrown overboard. Hence, many are flying with only about 5 quarts, recently many have become concerned that this might be a bit too little for a 550 engine, so they now keep 6 or 6.5 and just live with e increased oil “consumption” and the dirty tail.
BTW, some have reported good results with air oil separators and other “solutions” while others didn’t have muck luck with that. It also sems to be a little dependant on model and year.
What certainly helps is to avoid climbing at too high pitch angles (not above 10 degrees).
@Peter: this is what I was taught, in different schools, from small petrol engines to big diesels: oil level slightly below recommended max, all fine. All oil exceeding the maximum fill level will be thrown out. So actually, if you fill to 10 you will not be “using up” i.e. burning oil, you will be pushing it up the cylinders to be blown out (as Bosco already said). Sheer waste and not the slightest bit of advantage.
It’s a similar story on the O360 in the TB10 – anything above 8 gets thrown overboard straight away, 6-8 disappears in a couple of hours, and then the level stays at 6 for more than 20 hours. Usage does seem to be slightly correlated to altitude – I’m not sure it it just throws away more at high RPM/when pitched up, or if it genuinely uses more at higher altitudes.
I keep my oil at 5.5qt even though the POH contains 8qt as the top normal oil level. The reason is that the engine tosses out everything above 5.5qt but consumes virtually no oil once it’s at 5.5qt which is still plenty. I do my oil changes every 25h but I never add oil between oil changes.
As the engine ages, pistons tend to pressurize the crankcase and this makes the engine toss the oil overboard. For an engine you know well, it’s OK to take less oil because the chances of it suddenly burning a lot more oil and you running out of it on a flight is slim. For an unknown aircraft, I would always start with max oil.
Air-oil-separators are evil, stay away from them. Attach a small glass bottle to your crankcase breather and go on a longer flight. Then look what you have in your bottle. Imagine that stuff will be fed back to the crankcase which is what an air-oil separator does. Also these devices have very interesting failure modes and installation mistakes that can ruin your day. Never ever.
oil level slightly below recommended max
Yes but the recommended max for mine is 12.
Exactly. The point is that on many aircraft/engines, one has to go way below max to reach a point where oil loss becomes negligible…
Yes but the recommended max for mine is 12.
Oil sump capacity is a regulatory thing. The engine maker gives you a max allowable oil consumption per hour (which is a ridiculously high amount, like 1qt per hour) and the airframe manufacturer decides about the endurance. If you take endurance x max consumption, the remaining oil must still be twice the required amount per the engine manufacturer. The TB20 has ca 330l fuel and a big engine, that calls for a large sump.
The TR182 has about the same endurance and same engine but no space for the oil sump due to the retractable gear so Cessna got Lycoming to state the max allowable oil consumption is less, in an engine variant that was specifically created for that airframe.
The modest O-320 D2J of my C172 does the same.Pour 8 litres as dictated,it will spit out the first 2 litres immediately and remain with the 6 litres for the next 50 hours.It all has to do with crancase pressures.
I think the more relevant figure is the minimum amount in your POH, not the capacity. Obviously you don’t want to fly with less than the minimum specified in the POH (although with the certification margins that factor into that figure, it would probably be safe to fly with a bit less if you know your engine and act accordingly), but there’s nothing to say that you have to fly with more. Many engines have a level that they are happy with, and throw everything else overboard, which is both messy and a waste of oil.
On our IO-540, which is now on around 2400 hours, oil consumption is stable and we usually have to add around 5 litres between oil changes (50 hour). If we top up above about 6.5qt the excess just gets thrown overboard, so we just add 0.5 litres if the dipstick shows below the POH figure of 6 qts. Obviously if you top up to nearly full the oil consumption skyrockets, and you have to do a lot more cleaning!
