My understanding is that small planes generally use air-cooled engines. I am also informed that air-cooled engines tend to burn more oil than liquid-cooled engines, due to the sloppy clearances that must be designed into the piston/bore/ring fit in order to tolerate a relatively wide range of operating temperatures.
Is it correct to say then that small planes burn a lot of motor oil? If a car cruising down the highway burns (for example) 8 ounces of oil in 1000 miles, and takes 16 hours to cover that distance, then that’s 0.5 ounces of oil per hour. What number would I expect for a small plane in a reasonable state of engine health? Is oil consumption worse during warmup (when things fit really sloppy), or is it worse under high power (e.g. takeoff/climb), despite the engine having been warmed up at this point?
Moderate oil consumption for airplane engines isn’t necessarily a bad thing (see point #5 in the link below). You will generally have more oil burn in a piston aircraft engine than you will for a roughly equivalent car engine that produces the same power because of design differences. The amount of oil burn varies a lot by engine type and even for individual engines but it is nothing to be alarmed about as long as it remains rather constant. A big warning flag is when oil consumption changes significantly and quickly. Rates of oil burn that could be typical and healthy could be anywhere from a liter per 14 hours of flight to less than half that for something like Continental engine in a very small plane like a Cessna 150. Every engine manufacturer gives the typical rate of oil burn in the owner’s manual and checking the oil before every flight is part of the preflight checklist.
Starting the engine, especially if it has been sitting cold for a long time is the most stressful time for a small aircraft engine. That is why it is advised that owners of small planes actually fly their plane at least once a week and not let theirs become a hangar queen. Letting it sit too long can have all kinds of nasty effects because the protective layer of oil will eventually drain away and let rust and moisture creep in.
My Lycoming 0-320 ran Shell 50 wt. It never used a drop of oil between oil changes (50 hours), but it had < 200 hours SMOH on it. Older engines (higher time engines) use some oil, but not enough to cause a problem with a 3 to 4 hour flight.
I remember putting in one or two quarts per jet engine in a F-111 after a 3-hour flight.
I remember the guys on the piston engine T-29 bringing out a 55-gallon drum of engine oil with a hand pump. Of course a T-29 was not a small aircraft. When the left engine on the T-29 would start, the blue oil smoke would fog the entire fight-line for mosquitoes!
Q: Why did the US Air Force get rid of piston engine aircraft?
A: The Russians developed an oil-seeking missile.
No. I was an aircraft mechanic (crew chief) on F-111s at Cannon AFB NM and RAF Upper Heyford UK.
As a mechanic on them, I thought that they were crap. Former F-4 crew chiefs thought so too. Many, many maintenance-hours for each flight hour. I later worked on T-39s (military version of the Sabreliner) and C-9As (military version of the DC-9) and they were a joy to work on. However neither of them could drop bombs.
FWIW, oil viscosity needs to be higher in an air-cooled engine due to the larger clearances, so capillary effects keep it in place.
The big piston engines on 1930’s-50’s airliners could burn oil almost by the barrel. It wasn’t unknown for a transcontinental flight to have plenty of fuel but still have to make an oil stop enroute.
In my experience most of the oil loss from an aviation engine (opposed 4, 6 or 8 cyl) is from the vent tube. Not sure if it’s true across all makes but the difference between a quart over a year and a quart every 8 hrs of flight is an oil separator.
Do small planes burn much oil??
They do if they are on fire.
How worn is the engine?
I had a plane that had a 2 hour flight max due to an oil leak that would make the windscreen impossible to see through. I did get pretty good at landing that plane with the side window open.
My experience is certainly that they burn more oil. When I used to fly Islanders and Shrikes we carried oil in the back because it was normal to have to add some after a 5-7 hour flight. Jet engines use a bit as well
I’m not considering any specific engine; I’m trying to grasp what chemical constituents would be present in emissions plumes from general-aviation airports.
If you don’t know much about engines there’s an important point to made regarding the difference between two-stroke and four-stroke engines. Two-stroke engines (which are pretty much only used in experimental aircraft, IOW ultralights) by design use & burn oil mixed in with the gasoline. They don’t have crankcase oil with a dipstick, the oil is either premixed with the gasoline before poured into the plane’s fuel tank or, on more sophisticated two-strokes, they have separate oil & gas tanks and the oil is injected into the gas inside the engine (called ‘direct injection’). In either case the oil’s purpose is to serve as a lubricant but because of the more simple nature of the engine design it also gets burned with the gasoline in the process.
Again these are only used in small, experimental aircraft. I don’t think any Cessnas or general aviation aircraft use two-stroke engines (there’s an upper limit to a two-strokes power & efficiency).
If you wanna get technical ***all ***jets and turbo-props burn nothing but oil! (Jet-A, diesel, kerosene and home heating oil are all very similar, just different purities…)
If you’re considering oil consumption from an economic POV, remember that most aircraft recip engines get 100% fresh oil every 50 hours. That’d be the equivalent of changing your car oil about every 1500 miles.
So even if you’re not burning any at all, you are still consuming a quart every 5-10 hours depending on your engine’s sump size. Last I checked, aircraft recip oil was pretty spendy compared to generic automotive 10W30.
ETA: Hadn’t seen the OP’s clarification when I wrote this.
Cessna also has a new compression-ignition piston engine that burns jet A, not diesel. The Skylane JT-A. The awesome thing is that it lacks the normal duel magnetos found on other General Aviation singles and twins.
Jet-A and diesel fuel are pretty much the same thing, and so is heating oil. The attraction of diesels in light aircraft is that Jet-A is available practically anywhere, while 100LL gasoline is not and is on its way out entirely someday fairly soon. Nonreliance on century-old ignition technology is nice too.
Check my math here… Figure a Skyhawk averages 130 smph, and it flies for 50 hours. That would be an oil change after 6,500 sm, wouldn’t it?
The problem with Cessna Diesels is that the Skyhawk that was just introduced with the engine costs almost half a million dollars. Anyone who can afford to spend half a million dollars on an airplane isn’t going to buy a Skyhawk!
It’s the Turbo Skylane JT-A I was talking about. I don’t know if that’s going in the Skyhawk or not. But a 227 HP Skyhawk would be a real treat to fly, probably climb like a rocket on a mission.
My calculation was the other way. If you had to change car oil every 50 hours, that’d be after about 1500 miles of driving. Thirty MPH being a decent long term average for most folks’ mix of city / highway driving.
My point being that the time-based changing requirement for aircraft oil changes causes far more oil consumption than one would expect from automotive common experience. And that time-based changing often consumes more total oil than is burned or blown out the breather during engine operation.
I agree your approach would make more sense if we were considering how much oil would be consumed doing a particular mission, say NY to LA & back.
Had the OP initially asked us the question he really wanted answered, we’d all have come closer to giving him useful info.
Miles are totally irrelevant to an aircraft. It’s always hours of operation. A wise pilot changes his oil based on hours flown, or time since last change. Acids form in the oil under certain circumstances, so changing it prolongs engine life for aircraft operated less often. Same probably applies to automobiles.
