Toluene is used in auto fuel for an octane booster but is not compatible with Buna N O-rings.
Where I get my ethanal free fuel the distributor says that it is 50ppm Toluene.
I haven't researched it yet.....but what's the deal?
A while back I had an o-ring swell up in my fuel selector valve, it restricted flow to about 12gph from one tank. Was it from the Toluene?
I test my fuel regularly and know I haven't run ethanol through it.
Does Toluene fit in with the auto fuel STC?

Not airplane related, but I recently had buna-n o-ring problems in my powerstroke because the ultra low sulphur fuel would make them shrink/harden. I swapped them for viton o-rings and haven't had any issues.

Sure glad you posted. Just think of the bad rap ethanol has gotten and probably as much or more the gasoline was the problem. I know of a fuel selector that has had E10 going through for almost 5 years and it doesn't leak. That o-ring is way older than 5 years also.

It sounds like toluene is also in 100ll, maybe it's not a big deal?

Here is a compatibility guide.
http://catalog.gpi.net/Asset/Chemical-Compatibility-Ver-6.pdf

Viton (a perfluorelastomer) is fine in toluene. Kalrez is actually better, especially at elevated temps, but the cost does not really pencil out.

McMaster.com

I ran into the problem when folks were replacing the primer with the wrong o-rings- and made the primer unusable.

We use Viton 75 O-Rings in our Gascolator's specifically because of this exact problem. Viton 75 is impervious to all known fuels including straight alcohol, diesel, jet A, etc...

Brian.

We use Viton 75 O-Rings in our Gascolator's specifically because of this exact problem. Viton 75 is impervious to all known fuels including straight alcohol, diesel, jet A, etc...

You wonder why they even make the other kinds that aren't impervious to everything.

http://www.marcorubber.com/material_chart.htm

This is a materials chart showing basic compatibility with fluids for the different compounds of O-Rings. Viton 75 is not very good for Steam or standard automotive type brake fluids.

If you really want to do your research you can go here http://www.marcorubber.com/compatibility.htm and look up the particular fluid in the drop down list and see what rating the O-Ring is at for that fluid. On this list Viton A is listed as a #2 (scale 1-4) at a 10 to 20% swell for Toluene. Butyle is rated 4 - not recomemded.

Brian.