Tuesday, October 02, 2012

1 Quart less than normal for flight school


One of the bits of "common sense" I've heard for years is that you should run an engine with 1 quart less oil than nominally "Full", because "it will just throw that extra quart out." I've never taken verbal or confrontational exception to such a statement, but it seems counterintuitive to me that a manufacturer would specify a full oil level (say 6 quarts) knowing that the engine would purge itself of that extra quart.
So, what's your take on this bit of advice from the old-timers? I don't want to install 6 quarts of oil only to lubricate the ramp or the countryside with the superfluous quart. And I want to provide our club members with the best information available as we begin to operate this new, and expensive, engine. 

I believe it is good common sense to teach students (and instructors) to make sure that the engine has the manufacturer's recommended amount of oil in the engine.    There may be a time when that last quart of oil is the only quart of oil.

Teach the student to reference authoritative sources for information and be sceptical of rat chatter from the hanger. For engine operation this is the engine manufacturer's operating manual; for the airframe this is the airframe operating manual. There are numerous other resources that the manufacturer provides.  Not that there is not good information out there but there is also awful information that makes it difficult to decide which is good and which is bad.

One other error I see is that a specific recommendation might be good advise for some but not all. A good example of this is engine leaning. There is not one way to lean that is correct for all engines or all pilots in all circumstances. Another example is your question about 1 quart down; 1 quart down on a 12 quart sump is a lot different than 1 quart down on a 6 quart sump. Given that an engine can develop a problem and burn easily 2-3 quarts an hour without the pilot being aware; this could lead to disaster. Beware of blanket statements -- there are always exceptions.

Students and their instructors should start out with good habits. As they become more experienced they can then explore some of the other methods.

1 comment:

  1. John:

    I'd add that the best advice for an engine you "live with" may differ from that for an engine you're "just visiting".

    My 182's Continental O-470U (about 1,600 hrs SMOH) has a 12 qt sump. The Type Certificate Data Sheet says that the minimum oil for engine operation is 6 qts.

    I've lived with this engine for over 1,000 hours. I know that if I service it with 12 quarts it will be down to 10 within 10 hours and then sit there, maybe consuming one qt over the next 40, or 2 qts at most. So I service the engine with 10 qts and usually add 1 qt some time around 30 hrs.

    I recognize that the engine can change and start consuming oil at a greater rate, but I'm confident that since I know the engine's behavior pattern I'd see something unexpected and react appropriately.

    In contrast, a student pre-flighting a flight school aircraft has no feel for what's normal on that engine. Therefore she/he should be conservative and add oil any time the dipstick reads more than a quart below "nameplate" capacity.

    Thanks for the thought-provoking post. I always look forward to your ideas.