Practical Sailor contributor, Chesapeake Bay sailing blogger, and chemistry guru Drew Frye is still in the lab with his beakers, test tubes, and mason jars investigating fuel additives, this time fuel storage additives. Frye has covered a range of fuel additives before, beginning back in 2008 with an article focusing on the effects of ethanol in gasoline. Our current test involves both gasoline and ultra-low sulphur diesel.
The fuel storage additive study is proving to be a tricky one, partly because treated gas is capable of being stored for very long time in the right conditions. Samples in our accelerated lab testing were still within the recommended octane specifications after the equivalent of two years of storage. Diesel, in the right conditions, can be stored even longer and still stay within specification.
Sometimes it is not what has been added to your fuel that matters, but what is missing. The most obvious difference between gasoline and diesel during our vented aging tests is that gasoline samples evaporated and required replenishment at the mid-way point. Studies by BoatUS and the EPA have shown that anywhere between 5 to 20 percent of the contents of a portable or installed polyethylene tank can vanish during the course of a year, the result of breathing losses and permeation. The remaining fuel is lower in octane, contains fewer of the volatiles that are so essential for easy starting, and has reduced solvency for gum and varnish. It often looks perfectly good-most of our samples did-but is perfectly rotten and potentially harmful as fuel.
There are several things you can do to ensure that fuel doesn’t go bad over the off-season, or during periods of long-term storage.
- Reduce permeation. New EPA requirements for low permeation jerry cans, plastic tanks, and hoses are a blessing. The loss of vital volatile material is reduced and odors are reduced. However, our experience with the new jerry cans and portable tanks has been disappointing. Most of the designs we’ve tried have serious flaws; we can only hope the market place will sort that out. Metal tanks have zero permeation.
- Store in a cool place. Keep jerry cans out of the sun whenever possible.
- Vent filters. The EPA mandated carbon filters on new boats and aftermarket silica gel filters reduce water absorption and reduce breathing losses. Over a typical 10-years life, these filters can pay for themselves in saved fuel alone (we checked the calculations-depending on the boat you can expect to save 1-3 gallons per year), before factoring in reduced engine problems caused by corrosion and varnish. (See Practical Sailor January 2013 and, for diesel fuel, January 2014.)
- Keep the tank full. A full tank will not breath, and fresh fuel renews the volatile content. By full tank, we mean the tank is filled to the “safe fill level,” which allows for expansion. This is the working definition of full, since a fuel tank should never be filled above the safe fill level, which is commonly defined as 96% for stationary tanks and not more than 90% for mobile tanks (depending on design). In fact, we have witnessed tanks overflowing because they were overfilled and temperatures rose. It’s a mess, and environmental problem, and a fire hazard.
- Keep the vent closed when not in use (dinghy engines only). Water absorption and evaporation affect small tanks more quickly.
- Run the engine often. The silence of wind power is nice, but gas does not keep.
For more on fuel additives, check out the previous posts, Fuel Additives: Snake Oil or Good Science. which has some additional links. Diesel engine owners will want to read the article in our January 2014 issue Diesel Fuel System Maintenance Best Practices.
It was interesting when you talked about how filters need to be vented to reduce water absorption. According to my knowledge, having the fuel polished is also a good way to save money by helping the filters last as long as possible. I enjoyed reading your article and learning more about fuel storage optimization, so thanks for taking the time to share!
I have this issue right now. I’m glad to know that it’s better to leave the tank close to full. I guess, darn the luck, that I simply have to use the boat often to keep the fuel fresh.
In a former carrier I worked as a licensed marine air cooled engine mechanic. The number one job I did was rebuild carburetors because of spoiled fuel. We in North America can blame California who needed to mandate high pollution standards. The result was much finer jets in carbs and for a while non rebuildable carbs. I rebuilt carbs so much I started adding a bottle of fuel stabilizer with every carb rebuild. My advise put it in all your gas as soon as you go to the pump. If it’s in your jerry cans it will also be in your recreational engine tanks. Now diesel that is another animal in itself. The main problem with diesel is it contains water. There are bacteria that can grow in that water in diesel fuel. It makes a filter plugging engine stopping sludge. Service your fuel filters with regularity! I use FuelRite additive. I have no business affiliation with them. I’ve done my research and I believe it to be the best product. Home heating oil suppliers, hospitals and industries that rely on back up diesel generator power also use it.
I’m interested to know if sailors ever use the common industry practice of fuel tank “inerting” (adding a layer of N2 or other combustion suppression gas to the space above the fuel in the tank) as a means of dealing with residual fuel onboard?
My own experience using SF6 (sulferhexafloride) for hot work fire prevention makes me think such a practice would be beneficial and protective of the boat and the fuel quality. Seems like a good SF6 blanket will keep the volitiles in suspension (acting as a preservative) and eliminate fire hazards.
I add an ounce of the ethanol treatment to every 10 gallons of fuel in my 125-gallon fuel tank. This habit ensures that my boat engine maintains its top performance. Based on my friend’s testimony, it’s also an additive for small engines to avoid problems with ethanol.