Someone gave me 1 gal. 15% fuel , but the cap has a1/4 In. hole in the top for at least 1 1/2 years.
can I mix with fresh 15% ?

I wouldn't use it in any form. If the bottle wasn't tightly sealed it's going to have absorbed moisture from the air and will no longer be any good. Moisture is the enemy of fuel and all fuel should be stored in sealed bottles.If you mix it with "fresh" fuel all you are going to do is ruin the good fuel.

Ken

DON'T Throw it out its GOOD......for killin' weeds in the road at the field

Run it. If the engine runs fine well then the fuel is ok. If not, use the fuel for cleaning parts..

My guess on what happened is that most of the methanol has evaporated, as well as some of the nitro. So you have a fuel with a lot of oil. I don't think I would routinely mix it with new fuel, but maybe add a little to new fuel for break in, or wherever you would want high oil content.

I was going to suggest saving it for cleaning gummed up engines, parts, etc...but RVman kinda beat me to it.

I have my doubts though that an engine will run adequitely on it.

Our fuel attracts water rather well. Nothing is more fustrating than trying to get someones nice engine running with bad fuel. I was part of a situation at the field one spring where several guys were helping with an uncooperative engine for over an hour. Finally someone asked how old the fuel was. The looks that guy got were not pretty!

<span style="font-family: Comic Sans MS"><span style="font-size: medium">so what if the fuel is maybe just a couple of years old but kept sealed with no holes or sunlight, but left to sit on the ground? a guy i used to fly with told me a couple of years ago, that if you left the fuel sitting on the ground, it would ruin it. kind of like with car batteries on the concrete. now I know, there's no "battery" properties with the fuel, but it has been sitting on the ground in my nice cold, dark garage for a couple of years. is that some cornball jazz or what? and yes, i also make up my own words and phrases. i think it's wildcat 10%. it still smells really strong and burns really bad in the nostrils. someone told me that...i used a tank of it for an engine run and it seemed okay, but that doesn't put a true load on the motor as if it were pulling a plane through the blue. or would it be more of a load since it's stationary? that sounds more correct. i don't know...</span></span>

If it's in a sealed container it should be ok. Routinely, though, I go through it pretty well and don't have it around that long. I did have a couple of gallons of S&W 15% a few years ago. I bought 16 gallons of the stuff at the beginning of the season and at the end, I had two gallons left. It sat in the closet for the Winter season, then in the Spring, I used it like it was new. No problems. However, it was in sealed containers, meaning never exposed to the sunlight or air/moisture contamination.

In this case (the OP's situation), that hole in the cap is the issue. No matter the size of the hole, two things can and most likely did happen. Our fuel is Methyl Alcohol with Nitro Methane, plus some sort of oil blend. The oil won't evaporate but the methyl alcohol will. And, Methyl Alcohol is an alcohol and alcohol absorbs water. That is the double whammy here.. contaminated fuel that has had some of the alcohol content evaporated away.

As RCKen suggests, don't use it in your engines. There are other uses for it. I used some old and suspected contaminated fuel to start the fire in my fireplace. Works just fine.

CGr.

Your old fuel will work great... for taking epoxy glue off your hands and leaving you with a slightly oily feeling, or for cleaning permanent marking pen marks off monokote but there's not a lot else you can use it for. You can't even thin epoxy with it to fuel proof your firewall as the oils will stuff up the glue. As several people have pointed out our fuel is highly hygroscopic and very volatile with a low vapour point, so leaving it unsealed even for a few hours will quite possibly kill it, especially if you live in a humid area. And before you ask, no, there's no way to remove water from the fuel once it's in there. I've heard people talk about putting it in a freezer to freeze the water then straining the ice out, but it doesn't work as the H2O actually bonds with the CH3OH on an atomic level creating a whole new molecule (methyl oxide, if I remember anything from my high school chemistry) This is the same as not being able to freeze rust (ferric oxide) then chip off the ice to remove the water and leave pure iron. FYI, freezing vodka/applejack etc and straining out the ice DOES work, as there's a lot more water in these than can be dissolved into the ethanol.

I've also head of issues with leaving it on concrete floors, but that's an old wives tale (no offence intended to any old wives out there). If it does bother you though, feel free to keep it on a shelf.

Theoretically even sunlight shouldn't bother it too much, but UV light can do strange things to plastics (like the jug it's kept in) so it's best to keep it in the dark just to be sure, at least during long term storage.

As rightfully indcated above, DO NOT use fuel that has been left exposed to the air for any length of time.

The fuel absorbs water, and that causes all sorts of problems.


Sealed jugs that are kept out of the sun, can often be used without problems after many years of storage. While water may appear to condense on the inside of the jug, what appears is what is already within the jug, so it does not increase the amount of moisture in the fuel.

People have erroneously assumed that because heating and cooling can cause this condensation to form, AND because water in the fuel is bad, that it follows that leaving fuel on a concrete surface ( which causes this internal condensation ) will ruin it. That is not necessarily so.

However it is best to try to limit the amount of temperature change to assure the stability of the chemicals.

It has been said that temperature cycling will make fuels with castor oil run better. I have part of a jug of fuel that is about 30 years old. I run some of it through an engine on the bench from time to time and it runs fine. I wish some one would run an experiment to see if the problem with open fuel is more water absorption or methanol evaporation. If it is water absorption the fuel sample should gain weight, if methanol loss the fuel would lose weight. Eventually it would lose weight as both water and methanol evaporate, I suppose.

Fuel absorbs water from the air, and the methanol tends to evaporate faster, so you may not see a large weight change initially.

I've had guys show up with fuel jugs with about 1/2 gallon of fuel, which had gone a week uncapped in a cool location, that could not start their engines with that fuel.

Once I flushed out their tanks and engines with fuel from a newly opened jug, no problems what-so-ever.


On the other hand I've seen people panic when they see a bit of condensation on the inside of a sealed jug I have...


Took the fuel, shook it, popped the seal, filled the plane, flew all day.