Topping off the fuel tank or running it dry

Maybe this question has been asked before but if it has I can't find it. I have a 25-hp Yamaha 2-stroke that I use pretty much all year. It's one of the advantages of living in the sunny south. So far at least I've been able to find 100% gasoline so the following question isn't as critical now as it will be when I have to go to ethanol. Right now I top off the gas tank after each trip in order to minimize condensation. It's usually no more than a couple gallons on a 6.5-gallon tank. I wonder if this will be the correct strategy after I begin to burn ethanol though. Topping off (often no more than a gallon) means that 4 or 5 gallons of old gasoline remain with the distinct possibility of going through phase separation and all the nasty things that can happen to the motor when it does. Would I be better to let the tank run down as low as possible before filling up or would it be better to keep topping off? For the most part I manage to get out on the boat at least once a week but there are times when I can go for several weeks without taking the boat out. I know I can use Sta-Bil or other gas treatments but I'm more interested in the topping off or running it dry strategy.

In your situation I say keep it full.

Ethanol "attracts" water more than 100% fuel. So it has been told to me that the leave it full method is not good. The more you have in there, the more water problems you could potentially have. So I would expect the run it (almost) dry is best.

While there are a few gas stations in my area that have 100% gas, I have yet to go out of my way to fuel up there. My boat has a water/fuel separator, so guess I have some protection there? The last time I changed filters, I dumped it in a jar and did not notice any water (the filter was on there for a year.)

One method that you could employ is to have a gas can at home that you keep full. If there is a long period of time between boat trips, then put that gas in your car. If not, put it in your boat.

Other than ensuring that I don't leave gas in my tanks more than say 2 months, I have decided not to worry about ethanol issues. Hopefully, it does not bite me one day! I doubt it though.

KRS

Look in to running a little Startron or Stal-bil in the fuel.

I use my boat year round but sometimes it does set for 2+ months at a time like it has recently. In CA our gas contains 6% ethanol. Whatever gas I have in the tank is what stays in there until the next trip. I haven't had a problem yet in 20 years of doing it this way. If I start having problems then I will start using additives to stabilize the fuel.

lckstckn2smknbrls said:

Look in to running a little Startron or Stal-bil in the fuel.

Click to expand...

^ Sta-Bil Ethanol - Gas Treatment For Ethanol Gas is a special blend for ethanol, if you are using regular Sta-Bil then you are not dealing with the ethanol issues.

A fuel water seperator is your best defense. The problem in marine applications vs automotive is we don't burn as much fuel on a constant basis and the biggie is they have sealed systems and we have vented. With our boats in wet environments, and vented, you add ethanol and suddenly it is soaking up all the water from the air around it.

So, use Sta-Bil Ethanol treatment, and keep it full.

Bufford

You're doing it right. Full tanks can't condense water from the air and rust (if it's a steel tank). Sounds to me like you are running the motor enough to keep the fuel fresh. The opposite is true for the outboard. If the motor will be unused for more than a few weeks, drain the carburetor to prevent varnish build-up. Running the motor 'till it dies doesn't do it.

By running it dry what I meant was that I use all the gas in the tank before filling up again, not pulling the gas line and letting the motor die. Sorry for the confusion. I also forgot to mention that in addition to running the motor at least once every couple of weeks and using only 100% gasoline, I also use a 10-micron fuel/water separator as well.

lckstckn2smknbrls said:

Look in to running a little Startron or Stal-bil in the fuel.

Click to expand...

That is all you need to do - full, dry or 1/2 way, the stal-bil will work. This is what the major boat yards do here for the salt water boats and the one guy i know has done 1000s of boats and never had a problem - and we use ethanol gas here

Captain Ahab said:

lckstckn2smknbrls said:

Look in to running a little Startron or Stal-bil in the fuel.

Click to expand...

That is all you need to do - full, dry or 1/2 way, the stal-bil will work. This is what the major boat yards do here for the salt water boats and the one guy i know has done 1000s of boats and never had a problem - and we use ethanol gas here

Click to expand...

That's what I needed to know. I'll run the 100% gas for as long as we have it, but when the inevitable time comes and we can only get the ethanol I'll go with the Sta-bil.