Diesel sitting in tank for years

[oft]

We had our 12 gallon tank for a Yanmar YSB8 replaced 16 months ago. The new tank was supposed to be around the same size but turned out to be 19 gallons. I topped up the tank to within 2-3 inches from the top (the new tank is mounted vertically and is approx. 24 inches high) last fall on the advice that it would help to minimize condensation forming inside (the boat is in northern Washington state). The problem is we really only use the motor to get in and out of the marina and after the entire season we've only seen the diesel level drop to about 5-6 inches from the top -- much to the shock and disconcertion of the nearby powerboaters. It's quite clear that if I top it up again (admittedly late this year), we'll end up having the majority of the diesel sitting in there for many, many years. So, is it better to not top it up each year (maybe every other year instead) in an effort to go through more old fuel or should I still top it up every year? Either way, are there any steps/precautions that should be taken in dealing with the diesel in there that will eventually be getting quite old?

Thanks.

[max-on]

We have a similar problem / question. My quick answer, and how I have addressed it (although this year I intentionally ran the engine a lot the last month and got the fuel down to 3/4 of the tank, about the same size as yours) is that it is not a problem unless it becomes one. I would use a stabilizer and anti-growth and cleaner additives at the end of the season, and make sure you have a quality fuel filter, check it regularly, and carry a spare filter. If the filter starts to get clogged, then I would think about addressing the question, until then, sail the boat.

[sailingdog]

Diesel fuel can last a long time, provided you keep the water out of the tank. If you have water in the tank, then you'll need a good biocide.

[Sailormann]

Drink more beer. This will require you to run the engine more frequently in order to charge the batteries which keep the beer cooler chilled. You will get rid of the diesel. I think you should try to empty it at least every couple of years.

[Hartley18]

If it's going to take years to empty the tank, then, quite simply, the tank is to big!

One solution used on standby generators the world over, is to fit a smaller 'day tank' (with sufficient capacity for a day-and-a-bit of typical cruising) somewhere between your existing tank and the engine with a 3-way valve to choose one or the other. For your typical days out, use the 'day tank' and on longer trips fill the bigger tank - otherwise keep it clean and empty.

[dohenyboy]

I like the day tank idea. How about keeping say 5 gallons in your tank and draining it into a 5 gallon yellow diesel can after each use. Fill up the can on the way home to keep it topped off. Lot easier than going to the fuel dock

[Idiens]

SD is right (again) - use some bio bug killer and maybe some water absorber additive.

Old fuel isn't so bad because the diesel engine recycles a lot of the fuel back to the tank, so the filter gets to see it more than once. Having a nice big easily viewable glass fuel filter bowl helps spot an approaching problem, as does a tank bilge with drain tap, but the latter is rare on many boats.

[k1vsk]

Or just have the fuel tested rather than theorize about whether it's good.

[Hartley18]

Originally Posted by k1vsk

Or just have the fuel tested rather than theorize about whether it's good.

The problem with having the fuel tested is that (a) it's not a free service and (b) the "bugs" (looks more like weed to me - whatever) can grow very quickly given the right conditions. The problem isn't limited to just diesel tanks either - it can block fuel lines just as quickly.

If you're going to leave the boat for more than a few months (eg. over winter), I would seriously suggest draining the fuel system and storing the fuel someplace less important than the boat, and if you never go out very far, use a smaller tank so that all the fuel gets circulated/filtered - not just the top layer.

Just my $0.02..

[Idiens]

Why should the fuel in a separate container be less vulnerable to diesel bug than in the boat's tank? The bug is bound to grow faster in warm conditions than in cold. It can probably grow faster in the rest left over in an empty tank than it can in a full one. I go with topping up to reduce air / condensation volume and adding additives.