In  eleven years of editing the newsletter nobody has complained about
 the
 oil  settling
 out of the fuel. There are a couple of reasons for this. When you  start
 the engine
 the fuel pickup in the tanks is at the lowest level  generally so you
 might
 get
 an oil rich mixture (as I recall oil floats on  the top of the fuel) but
 that is soon
 returned to the tank by the fuel  pressure regulator recirculating the
 fuel. At idle it
 recirculates as much  as 90% of the fuel flowing through the  pump.

 Paul Lamar


 The real question would probably be best answered by those engineers
 closely associated with 2 cycle oil and it's miscibility with aviation
 or other
 fuel.

 Oil either mixes with fuel and stays suspended (dissolved for want of a
 better word) or floats or sinks. It really can't do all three things.
 It is
 possible that it falls out of solution and then either one of the
 other two
 is  possible.  (If my limited knowledge of physics is still in tact.)
 If it
 floats, it will not collect at the lowest part of the tank (the sump)
 yielding  an oil rich mixture. If it sinks it will not float on top of
 the fuel
 (unless  the various densities of hydrocarbons dissociate with each
 other and
 based on  their  density relative to water they either float or sink.

 It might be an idea to, during your preflight, to vigorously shake the
 wings for two purposes. 1, to mix the oil, 2 to check the continuity
 of the
 spar.

 Just a suggestion.

 Rich

I have just tried this, 5 ml 2-stroke oil in 500 ml auto gasoline in a
glass jar. The oil goes to the bottom. Part does dissolve quickly but
the bottom half of the jar has all the color. The bottommost layer has
the darkest color. It takes some shaking to get a uniform color. If not
shaken, you will get a very oil-rich mix on starting.

Al Rees

That is interesting Al. Thanks for doing that. Let it sit for a week and
see if it settles out on the bottom again.

If the pump is pumping 20 gallons an hour
and 90% is recirculated on start up and there is 1 oz per gallon in a 30
gallon
tank that means there will be 30 oz in the bottom of the tank. Or.234
gallon
of oil. 18 gallons per hour divided by 60 is .300 gallons per minute. The
oil will
be sucked up in less than a minute and squirted back into the top of the
tank.

Check my arithmetic.

Paul Lamar

Paul,

A quick real world observation...  My Lancair holds 96 gallons, 47.5 gallons
per tank; I add 1 oz. 2-stroke oil/gallon for a total of 96 oz. oil.  If the
oil settled to the bottom of the tanks, even a little, I would expect to see
a cloud of blue smoke on startup. Since this isn't the case, I've
concluded to my personal satisfaction that oil settlement isn't a
problem.  My observation is null and void if you're burning something other
than 2-stroke.

Mark