Sport Pilot Talk

I’ve been using 91 unleaded, no ethanol fuel since my return from CA. I topped off 3 weeks ago and haven’t flown. I’ll prolly go up tomorrow and weather and temps are looking good.

What’s the longest you gone in between flights with auto fuel, before you needed to replace or add some 100LL?

I’m thinking a few months with non-ethanol gas vs with ethanol.

Ethanol free fuel will last a LONG time. I've read anywhere from 6 months to a year. 3 weeks is nothing to worry about at all. The last time I moved I didn't fly for about 6 weeks and didn't even think about the fuel. I never top off my tanks and I've never seen water in either tank. I use 93 OCT ethanol free fuel.

Fuel WITH ethanol is a whole other story. There's a report I read somewhere online that was written by an engineer at Chevron I believe and he talks about the shelf life of fuels. I think he's the one that mentioned that it's good up to a year.

ShawnM wrote:Ethanol free fuel will last a LONG time. I've read anywhere from 6 months to a year. 3 weeks is nothing to worry about at all. The last time I moved I didn't fly for about 6 weeks and didn't even think about the fuel. I never top off my tanks and I've never seen water in either tank. I use 93 OCT ethanol free fuel.

Fuel WITH ethanol is a whole other story. There's a report I read somewhere online that was written by an engineer at Chevron I believe and he talks about the shelf life of fuels. I think he's the one that mentioned that it's good up to a year.

Thanks Shawn, I know you can get separation with ethanol fuel, water, ethanol and the fuel over time.

8 -10 weeks and that's with something like Stabil in the fuel. If you go longer you may be pulling the carbs and rodding out the idle jets. As fuel sits even in a seal container it loose some of its octane rating and additives.
For longer than 2 months I would add a large percentage of 100LL to help stabilize it. Remember it has to be run a while to get that Stabil and or 100LL through the entire system. I wouldn't even think of 6 months. Drain it and out in fresh. That isn't that much.

Remember we're talking about airplanes and not a lawnmower or a car. Different animals and different engines and systems.

I have used fuel with ethanol that sat for 6 weeks with zero issues, no ethanol fuel will last longer than that. Remember also that fuel can sit in a tank for weeks or months before you even get it. I think people make this issue out to be more than it really is. Unless your airplane sits for several months at a time, I'd just check the fuel like you are supposed to on pre-flight and then fly the airplane.

I have seen 100% contradictory responses to this very question from reputable sources and since I generally don’t let my fuel sit longer than a week or two , on rare ocassions when I do let it sit longer ( as it has been the case now - 3 months ) , I just get rid of it and replace it with a fresh batch- not a big deal.
Better safe then sorry

Warmi wrote:I have seen 100% contradictory responses to this very question from reputable sources and since I generally don’t let my fuel sit longer than a week or two , on rare ocassions when I do let it sit longer ( as it has been the case now - 3 months ) , I just get rid of it and replace it with a fresh batch- not a big deal.
Better safe then sorry

That's the beauty of an online forum, ask 10 people and you'll get 10 different answers, pick the one you're most comfortable with.

Not a big deal? Draining fuel every two weeks because you didn't fly sure sounds like a HUGE pain in the a$$ to me. With my tiny drain valves I'd spend more time draining fuel than flying, no thanks. Again, do what makes you comfortable.

As Andy pointed out, how long do you think the fuel sat in the underground tank as the gas station before you bought it? I'll bet way longer than a week or two (depending on how bust the station is) and you dont see them out there draining the tanks and adding fresh, do you? Just sayin'.

As I mentioned before, I went 6 weeks and the plane started right up as it always did and the engine didn't skip a beat and performed as it always has. I agree with Andy that people make this into a bigger issue than it really is. I doubt anyone here could even tell the difference between fresh and month old fuel without testing the octane rating.

If you really worry about ethanol gas breaking down, you can always run 100LL in a Rotax 912.

The thing is , I know the plane will run just as it will run on 87 gas and frankly, may even run fine 80%-90% of time but then one day , based on some external factor,you may end up with silent detonations that you won’t be able to detect but it will slowly ruin your engine over time.
Why take chances ? I mean , I wouldn’t bother with two weeks but anything over a month , I wouldn’t chance it ...

Warmi wrote:The thing is , I know the plane will run just as it will run on 87 gas and frankly, may even run fine 80%-90% of time but then one day , based on some external factor,you may end up with silent detonations that you won’t be able to detect but it will slowly ruin your engine over time.
Why take chances ? I mean , I wouldn’t bother with two weeks but anything over a month , I wouldn’t chance it ...

I dont doubt that using "old" fuel all the time could possibly have some detrimental effect on an engine but the OP asked "what's the longest you've gone between flights with auto fuel?". I just feel that using fuel that's a month old or 6 weeks old once a year because you couldn't get to the airport because life got in the way isn't going to harm your engine nor would you notice a difference in performance.

My original point was that my 6 week old fuel didn't burn any different than the fuel I put in yesterday.

Again, it all comes down to what you are comfortable with and we each can make our own decision on how old is "too old" when it comes to fuel.

So where is the overly cautious guy who never trusts his instruments and always tests his gas tanks manually

Just kidding ... I am just parroting what I was told during my Rotax service class , that’s all

Warmi wrote:So where is the overly cautious guy who never trusts his instruments and always tests his gas tanks manually

Just kidding ... I am just parroting what I was told during my Rotax service class , that’s all

LOL, you bet your bippy I dip my tanks EVERY TIME before I start the engine. I just use my DIY rubber dipstick not a chemistry set.

ShawnM wrote: That's the beauty of an online forum, ask 10 people and you'll get 10 different answers

More like 11.

drseti wrote:

ShawnM wrote: That's the beauty of an online forum, ask 10 people and you'll get 10 different answers

More like 11.

Or 12 . . .

I have several cans of 93 octane ethanol-free mogas that have been sitting for up to 6 months. I had an extended period of “down time” due to personal reasons, though back in the saddle now.

My strategy recently has been to buy some fresh ethanol-free mogas and use it to mix with whatever “stale” fuel that’s been sitting when I fuel the plane. The resulting 50/50 mix should be fresh enough overall.

Not advocating for that, just putting my procedure out there for discussion.