I just got a boat that has not been registered for almost 10 years. The motors run fine on the gas but not sure if I still need to drain the gas or not. We have ethenol in the new fuel. There is about 1/4 of a tank.

Yes and no. Gasoline tends to lose oxidation and deteriorate after 4-6 months of non-use and will be for the most part useless after 1 year. While it certainly will still ignite and burn, the octane content for any engines useability is severely diminished as well the gas at this point may have also become both moisture laden with water vapor, and or particulate matter if it was not in a full and sealed tank when last used.

Any airspace in a gas tank or storage container (plastic or metal), allows for the collection of mosture over time which will also damage gas. Even sealed tanks such as your car have a pressure relief valve than allows some airflow in the tank thus allowing a vaccum to not occur in the tank. This small airflow over a long period of time, or during times of high air mositure, can lead to damaging moisture collection most primarily if the tank was less than full.

Also stored gas can collect particulate matter, rust, dirt, etc., which can clog fuel lines, filters, and can harm both carburators or fuel injectors. Old gas also creates what is called "gumming" or "varnish" which will cause clogging and sticking within carburators or fuel injectors regardless of ignitability. If this problem occurs you might be faced with a carb rebuild and or injector servicing which can become costly.

If your stored gas is a year or more old it is best to and cost effective just empty it.

if it's been sitting for 10 years it's not gas any more, you need to get it out and run new fuel and change the filters..which you may have to do several times...

I would get it out if it were me.

That was what I originally was thinking get it out and put it in yard trucks and so on. Then when I went up there the other day to warm it up before a very cold night I forgot the pony tank and it ran perfectly on the gas that was in there. I would of course not beat on it, just kind of run it out.

The real question IMO is what is going to happen with the old gas when it comes in contact with the new stuff. The motors are carb 420HP 454's by the way.

The only thing I'd run that gas in is the vehicle of someone I really didn't like.......I wouldn't put it in my lawnmower!!!!

I wouldn't run fuel if it was 2 years old let alone 10, get it out, and if your not real fond of your truck, put it in it. I have heard that old gas is a good weed killer.
larry

Assuming it is 10 years old I would think it would be like finding a 1/4 full open coke can dated 10 years ago and then fill it up with new coke. Would you drink it or give it to your neighbor?

Ok so I pull out the gas. There will be a little bit left in the bottom of the tank of course. What are the chances that the old gas will cause issues when I fill the tank back up with the new crap.

I would change the fuel filters before you run it any more they will rust inside just sitting over the winter. Then change them again a short while later. And keep a spare set on the boat with a filter wrench just incase. Filters are cheap , carb rebuilds are not. Just my .02 Jeff