Re: Gas in oil question for Chemical Engineers

["Rich Wagner" <drsavage@domain.elided>]

Al wrote:

>While I was working as a mechanic there was a popular belief
>that under the right conditions, high or operating temperatures, this
>gasoline/oil combination was more succeptible to boil off or evaporate,
>lowering the diluted lubrication level in the sump.  I have no idea
>whether this is a reasonable concept or not.  Gasoline does disappear
>when exposed to the atmosphere or to heat, but is it capable of
>affecting oil as well when combined with it?

First Al, I must admonish you for submitting a car-related post to the
Digest.  Remember, we mustn't consume bandwidth that others may need to
talk about guns.  Naughty, naughty.

Gas does indeed evaporate from the gas/oil mixture, without damaging the
oil, given a high enough temperature and enough time.  There's the rub. 
(Pun intended.)  With gas diluting it, the oil is thinner--lower viscosity.
 The question is, will the gas evaporate, and return the oil to its normal
viscosity before any engine damage can take place?  If the oil is too thin,
you might see damage immediately following start-up.  If it's just a little
thin, maybe the gas will evaporate before the engine really gets down to
work, and you'll get away with it.  Judging by the time it takes for the
oil in my GTV6 to warm up, I won't hold out for the latter.  If you're not
a gambling man, it's always best to eliminate the gas intrusion problem,
and change the oil.

A great many reciprocating aircraft engines were manufactured with an oil
dilution system installed.  In cold weather, the pilot would dilute the oil
with gasoline by turning on a pump for a few seconds.  As the engine warmed
up, the gas would evaporate.  This system apparently worked, because I have
yet to hear any "And there I was..." stories about it.


Rich Wagner
Montrose, CO
'82 GTV6 Balocco

------------------------------