Great info, nicely done test.

Jeff York

On Fri, Sep 7, 2018, 12:34 PM Jeff Scott via KRnet <>

> I thought I would make a followup report on the Mogas testing I have
> conducted and the little bit that I have learned from it.
> I attached a photo of the same five jars of fuel after a month of soak
> testing various parts that might be in the fuel system with some surprising
> results, but more importantly perhaps an additional test methodology to
> verify Mogas fuels for airdcraft use.
> In each jar, I place a new O-ring.  Then I worked some pipe dope
> (RectorSeal) into the threads of a 1/8" male pipe fitting and allowed to
> cure for 24 hours before placing into the fuels.  Then I laid up a single
> sheet of tooling glass with aeropoxy and peel ply squeegeed out as thin as
> reasonably possible and allowed to cure.  After curing, I cut the fiberglas
> into test strips and placed into the fuel jars for soak testing, one strip
> with peel ply still on it, and one strip without and only one end of the
> strip submerged in the fuel.
> The fuels in the picture are 1) 100LL as a control, 2) local
> Conoco/Phillips brand 3) local unbranded independent fuel  4) local CITGO
> branded fuel, and 5) local Murphy oil fuel that damaged my fuel systems as
> my second control.
> Testing:
> The O-rings really don't show enough change to quantify at this point in
> time.  I'd like to think I can feel some slight differences, but it is not
> sufficient for me to draw any conclusions as to damage to the O-rings at
> this point in time.
> The fiberglass test strips in the three yellow colored fuels (3, 4, & 5)
> and definitely showing signs of softening and degrading.  When removed from
> the fuel, it is visibly obvious which end of the test strip was submerged
> in the fuel and the submerged end is starting to soften and the resin is
> thinning between the weave of the glass.
> The pipe dope testing was very quick and probably the most telling.  Jar
> #5 dissolved the pipe dope from the threads of the fitting on contact.
> That test was completed in a matter of seconds.  Jars #3 & 4 both dissolved
> the pipe dope as soon as I swirled the jar, so that testing was also
> completed in a matter of 20 seconds or so.  Jar #1 (100LL) and Jar #2
> (local Conoco/Phillips) neither one attacked the pipe dope on the threads
> of the pipe fittings.  After a month and repeatedly swirling the fuels,
> Jars #1 & 2 still have the pipe dope intact in the threads of the
> fittings.   In the attached photo, I had just swirled the 5 jars.  The
> cloudiness in the three jars to the right is caused by the pipe dope in
> suspension in the fuel.
> After a one month test, I think I have a winner for a Mogas I can safely
> run in my planes.  The local Conoco/Phillips brand fuel seems to be just as
> innocuous to the various fuel system parts as 100LL.  Of course it is 91
> AKI fuel with no alcohol and no lead, so will get mixed with 25% 100LL for
> the time being to maintain the optimal amount of lead in the fuel for my
> engines.
> In conclusion, based on the simple testing I have done here, in addition
> to testing fuel for alcohol, I would also take a sample of the fuel and
> test it against a pipe fitting with some dried pipe dope to see if it
> attacks the pipe dope.  If the pipe dope readily dissolves into the fuel,
> you wasn to consider whether you want to run that fuel in your plane as it
> may eventually wick it's way through any doped pipe fittings, may attack
> any composite parts in the tanks, and may cause problems with rubber or
> neoprene O-rings or seals in the fuel system.
> For those of us with Epoxy resin based fuel tanks, this is probably doubly
> important.  I will say the slosh compound I used in my KR tanks some 22
> years ago did save them from damage from the aggressive fuel I used,
> otherwise I would also be cutting the tanks open in it as well.
> I have not yet repaired the tanks in my SuperCub Clone.  I have been
> waiting for cooler weather here in AR.  I anticipate getting started on the
> repairs after I return home from vacation following the KR Gathering.  I
> will post photos and descriptions of what I find after I cut the tanks open.
> -Jeff Scott
> Cherokee Village, AR
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