stale fuel vs. tank condensation

[REO]

Our Albin 27 has a 100 gallon stainless steel fuel tank that was replaced in 2011. When we replaced the engine last year the manufacturer (BetaMarine) recommended that I use fresh fuel for initial start up. I drained the tank and put in about 20 gallons of new diesel. Family commitments and good fuel economy dictate that I will use only about 15 gallons of fuel each year for the next several years. Should I fill the tank and risk having old fuel in the future, or keep it mostly empty and risk condensation?
The boat is stored in a metal building in Northwest Arkansas where the temperature varies from 10 to 110 degrees. I have considered removing the fuel filler cap and rigging up a fan to get some fresh air into the tank during layup, but wonder how much air will actually flow in and out through the small vent. Any suggestions appreciated.

 

[O C Diver]

Fill the tank up each year if you are worried about condensation. Diesel fuel will easily last more than a year.

Ted

 

[REO]

I agree that a year or two isn't a problem. My concern is only using 15 gallons a year means some of the fuel will be 6 years old. Maybe the 15 gallons if fresh each year solves the problem?

 

[O C Diver]

If you want to do the math, think you will find the theoretical level of old fuel in your tank at:

25% after one year
6.25% after two years
1.6% after three years
0.4% after four years.

If you really want to eliminate the problem, set your tank up to be drained at the end of the season, and refill it with fresh fuel before winterizing the boat. I'm sure you can find someone to take the 5 gallons of fuel.

Ted

 

[REO]

I think I wasn't clear enough. The tank holds 100 gallons. If I fill it I will use and replace 15 gallons each year. It becomes a complicated mixture of new and old fuel of various ages. Maybe I just need to live with the diluted mixture of new and old fuel. We had a sailboat that had a similar issue, and never had a problem with fuel that could have been partially 6 years old.
I did drain the fuel once. At today's prices-ouch-, I think I'll take my chances on the other options.

 

[jleonard]

I think you are thinking too much. Diesel doesn’t get stale like ethanol gas does. Add some Startron or similar to the tank if it makes you feel better.
You’ll be fine.

 

[REO]

I think you are probably right. The engine seller got me spooked. I have a fuel polishing system set up, hopefully that and fuel stabilizer will keep the fuel in good shape.

 

[jgwinks]

There's other threads here and other forums where people have used 20 year old diesel with no problem. I don't think I'd stretch it that far but the point is it basically doesn't go bad. Can get contaminated with water, dirt, bugs etc but you have filters for that and it's preventable. Modern gasoline's only good for a couple months for a comparison.

 

[REO]

Thanks for the advice. I'm going to fill the tank. Are all the name brand stabilizer additives about the same?

 

[Giggitoni]

Fifteen gallons per year? I wouldn’t be able to get home from a typical day trip until the following year!

 

[REO]

One of our previous boats was a Silverton 36 with 2 big gas guzzlers. I figured that we got about 4000 feet per gallon, so I know what you mean.

 

[Doodie99]

Fill it and don't worry.
I just brought a boat out of hibernation with full tanks of diesel from 2002.
Thinking if would have nasty fuel i drained the tanks completely to find a shiny fuel tank inside. it appears the fuel had been treated and i treated it last fall but it starts and runs well. It may smell a little more but diesel from 2002 had more sulfur in it. IMO the less air in a tank the less it with get condensation.