Yes, I'd compare the two specifically to point out the differences instead of similarities. Even the starting point is different: most modern car oils are almost invariably full synthetic.mallcott wrote:1: We need to be careful with too much cross-fertilisation of the design and construction of aviation versus. automotive oils. While there IS crossover, there is also considerable dissimilarity in the blends - even when the headline technical information would apparently indicate a high degree of commonality.
Yes in principle, and there have been advances in aviation oils as well. While they hardly are state-of-the-oil-art, older airplane manuals do contain some subtle clues in their operating procedures which in particular make sense when realizing that the engine oils from the bygone years really weren't such like AeroShell 15W-50, and coagulation even in relatively mild temperatures could have been an issue.mallcott wrote:2: Aviation oils will tend to work in a far greater range of temperatures than auto oils, and are surely compiled and manufactured to suit the specific requirements of the aviation industry. But there is a caveat: Modern aircraft engine oils and modern engines go together because they're designed that way. Aviation oils have to have high stability over long periods of non-use, but only for short periods IN use - 50-100 hour change intervals are still the norm, while your car might go 2 years between oil and filter changes, with near-daily use the norm.
When it comes to the oil change intervals, there are other aspects that come into play than the oil's stability on its own, which typically is not an issue over the regular change intervals. The interval is not short in hours only: Lycoming suggests a maximum of four months in between the oil changes. So does Continental, I think remembering. The issue is mainly with the contaminants these oils tend to collect (by design), moisture combined with bypassed combustion products for a big part. For many airplanes, if only it was followed, the 4-month interval would be the determining one instead of the hour-based one. For a much-flown airplane, where good engine management is employed, I personally wouldn't see a problem in extending the oil change interval to 100...200 hours, instead of common 50. But of course, one would need to ask why to do that. Oil changes are the cheapest maintenance. In similar sense, I see no point in oil change intervals that many automobile manufacturers promote (indeed, certain engines have ran into issues when these are followed): why to get cheap on frequently changing $/€50 oils with an expensive engine?
In aviation world, there is also that the filter inspection (if performed, of course!) obviously coincides with the oil and filter change. The oil and filter content analysis give a look into the engine's health, and frequent sampling is only better. While if I had a constantly flown airplane, I wouldn't obsess about the 50-hour interval but surely would recommend it in any case.
-Esa
, but let us get a bit behind the point. With that hypothetical high-time airplane btw, I mean one accumulating really high time when compared to typical GA, as in, say 8 hours a day for example, for some time span. Say, during that operation we wanted to change the oil every two weeks. That is, approximately every 112 hours, putting us into aforementioned range.. or maybe three weeks, which would mean 168 hours. The time the oil sits in the engine won't get very high if we for some reason wanted to skip the 50-hour check and go straight to the 100 for instance. For sake of it, let this hypothetical operator go to maximum insult, and do the oil change every 3 weeks / 168 hours. (To underline, I would not suggest this! Only for discussion, so to say.)
Seriously tho, I didn't know about it.