I hopefully will be in the situation where I need to buy some diesel fuel. I have been buying diesel fuel for many years, but only buy about 30 gals at at time on average. With a 40 gal tank, I don't go through much fuel and it sits around a long time. I have always used a fuel stabilizer/biocide.
Now I am looking at buying fuel (and burning fuel) in much larger quantities and could use some advice. I have read through all the threads that I can find here and boatdiesel.com but am still a bit confused.
Questions:
1. Is it "better" to fill up the tanks and keep them topped off, or is it better to only take on the fuel that would be used in a reasonable amount of time?
2. What is "reasonable" in #1?
3. Is using a fuel stabilizer/biocide reasonalbe?
Opinions welcome.
No doubt there's a lot of snake oil on the market where fuel additives are concerned. I believe you could bottle diesel fuel or kero, add some dye and make claims about smoke, fuel economy and algae and it would sell. And for the record, algae is virtually never present in diesel fuel, as a plant, it needs sunlight to carry out photosynthesis, of which there is precious little in the average fuel tank.
Having said all that, there are additives whose claims are reasonable, and they do work as advertised in my experience. In all the years I ran a boat yard, in which hundreds of boats were winterized, I used StaBil for diesel and gasoline stabilization, I'm firmly convinced it works. Diesel fuel is pretty inherently stable, at least for 6 months to a year (although ULSD has reportedly reduced this somewhat). After that a stabilizer like StaBil makes sense, although you should not stabilize old fuel, i.e. don't add it after 6 mos.
If, however, water is present in the tank all bets are off, as it will support biological life (which is typically bacteria and mold based), which can wreak havoc on tanks and fuel systems. Biocides will kill these organisms, but it's a crap shoot as you can't be sure how much to use, and the organisms, being animal based, actually have skeletons, which accumulate at the bottom of the tank after they die, and those skeletons are abrasive. The byproduct produced by these organisms, hydrogen sulfide, is acidic and corrosive to metallic tanks and fuel systems. You get the point, water in fuel tanks is undesirable in so many ways. Removing the water, therefore, using a stripper tube or drain, is far more preferable than treating biological growth by which it is supported.
The other major issue that can affect diesel fuel is lubricity. Lubricity is an article unto itself, however, in short, even diesel fuel that meets ULSD S15 requirements (contrary to popular belief and many articles that have been written about it, the ASTM diesel fuel standard, D975, remarkably, does not include an adopted lubricity requirement, I've read the standard), doesn't meet the requirements of many diesel engine manufacturers. Therefore, using an additive such as Stanadyne Performance Formula All Season, which includes a lubricity additive
Performance Formula « Stanadyne Additives(they do offer a stand alone lubricity improver, as well), while not mandatory, is very good insurance. No connection with the company, (or StaBil), I just use it, and recommend it, with every fill up and have for years. Stanadyne is made by a company that manufacturers fuel injection systems, which, in my estimation, makes them trusted enough to formulate and offer a product of this sort.
Stanadyne and StaBil include a demulsifier, which encourages water separation from fuel, enabling it to be drained off or sucked out of a tank, while many other additives include emulsifiers, just the opposite, which encourage water to mix with fuel. If you have a water seperating fuel filter (or fuel tank water drain). It strikes me as counterproductive to attempt to force water to mix with fuel, and have it pass through filters and into injection systems. And again, not knowing how much water is present makes using an emulsifier a gamble at best.
Just my opinion. With the exception of anchors perhaps, few subjects are as contentious and strewn with opinions as fuel additives, and with good reason, so little is, or can truly be known about them without lab testing.