Originally Posted by Kilgore Trout

Ryan, my understanding after checking the Petersen website it that the O-540 has been tested with auto fuel, but that the PA-32 airframe itself is not approved. The Petersen website has two routes to check, one for the engine, and one for the airframe. Did not check the EAA (who also sell Auto Fuel STC) for approved compatability with a PA-32 with an O-540.

Petersen website here- Petersen Aviation


This is an interesting subject to me, mainly for the reason that Avgas in Juneau is horrendously expensive the last few years. It's above $5 a gallon there right now, and a couple of summers ago it was near $7 a gallon. Pretty painful in a Beaver burning about 25 gph. Had a very negative effect on my employer at the time.

I've got a PA-11 (C-90-8F) which I purchased the Auto Fuel STC for, and a friend has a C-172D (O-300C) who also did the same. Our problem is ethanol. The 11 has enough "soft" parts in the fuel system that I have never even been tempted to violate the STCs prohibition of fuel containing ethanol, and I hope my friend will avoid it also, as the old 172 has plenty of parts that I have concern about too. Things like fuel selector seals and o-rings. Those get goofed up and there might be a problem.

The concerns about future availability and price of 100LL and ethanol free auto fuel are big ones.