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Sea Savvy - Fuel additives: the smart choice

As marine fuel changes — shorter shelf life, ethanol-spiked gas, low-sulfur diesel — boaters must adapt

As marine fuel changes — shorter shelf life, ethanol-spiked gas, low-sulfur diesel — boaters must adapt

Fuel — and fuel additives — is the combustible issue along the waterfront these days. And I’m not talking just about the flash point of the new

Read the other stories in this package: Ethanol and winter storage   A sampling of fuel additives

ethanol gasoline, although in a technical sense flash point does figure into the equation.

First, some background. During my early days in the Bahamas many of the fuel storage tanks supplying the pumps in the out islands were perched high up on a rocky hill behind the docks. Getting the fuel from the tanker to these tanks was a bit of a problem. Some of the islands had water that was too shallow at the docks for the tankers to come in and offload. So the tanker might tie to pilings off the rocky shore and run a long, fat hose up to the tank.

I watched this operation once and came away a believer in fuel additives. The crew took a line ashore in the tanker’s aluminum skiff and gave the end to some guys from the marina. These guys started pulling, and soon the long hose was snaking over the rusty sides of the tanker and through the ocean. Eventually the hose made it to shore, and the crew began pulling it up the hill. Every once in a while they dropped it, and when they did I saw, to my horror, seawater gushing out. There wasn’t a plug over the open end — or if there was it certainly wasn’t tight. They got the hose to the tanks, hooked it up, and the tanker started pumping. It isn’t clear to me whether the marina paid extra or got a credit for all that seawater. I do know that I never got any credit for it when I filled my tanks.

Since then I’ve read the labels on a lot of fuel additives. I can’t say that I’ve gotten many clear answers. I used to just pull up to the dock and fill ’er up. Now I feel like I need a chemist, someone from a crime lab, and an inspector from the Centers for Disease Control. But what, me worry? All you have to do is Google “fuel additives,” and you’ll realize that there are enough on the market to make any tank of fuel fulfill your wildest dreams — or do they?

The bottom line is fuel is different today. For example, it has a shorter shelf life, requires stabilization, and a condition called phase separation can occur as a result of ethanol (if it’s been added), which can cause serious engine damage. And then there’s the issue of winter storage and what to do about the fuel left in the boat’s tanks.

So I thought I’d start asking questions. The following information comes from observation and conversations with industry experts. I also interviewed executives representing five well-known companies that make additives (see "A sampling of fuel additives"). Finally, I’ll give my suggestions on how to make wise decisions about fuel additives.

The issues

1. Fuel issues will continue to proliferate as we all try to figure out and do what is best to protect our increasingly fragile planet.

2. The type of problems you’ll have will relate to the type of engine you have. Obviously, a gas engine has some different issues than a diesel. But older engines may have different problems than new engines, and the engine brand may make a difference. Learn the issues for your particular power plant.

3. Changes in fuel formulation, such as the addition of ethanol, can affect its flash point, and this can affect efficiency and performance. If fuel ignites too quickly or too slowly to correspond with the timing, the engine won’t run as smoothly; it could knock, waste fuel, lose power and have a multitude of other problems.

4. Jerry Nessenson, president of ValvTect Marine Fuels (and a boater), says EPA regulations will require many marinas to sell low-sulfur diesel (500 ppm) by Oct. 1, although most will have only ultralow sulfur diesel (15 ppm) due to the lack of availability of the low sulfur variety. “[Both fuels] contain more moisture, destabilize very quickly and are more susceptible to bacterial growth than high-sulfur diesel,” he says. “The results are sludge and plugged fuel filters that can completely shut your engine down while at sea.” In addition to these problems, lower sulfur means the fuel has less lubricity. Proper lubrication is critical for certain engine components, such as the fuel lift pump, injector pump and injectors.

5. Some of the changes being made to fuel, such as ethanol and lower sulfur content, can contribute to deposits. Cleaning engine parts that are involved with fuel and/or the combustion process (injectors, carburetor jets, valves, valve seats, combustion chambers) has always been an issue. Carbon and gum deposits make engines run less efficiently, waste fuel, increase emissions and cause other problems.

6. Moisture in fuel causes many problems. Obviously, if there is enough moisture, the fuel won’t ignite and the engine is damaged. But there are more subtle issues. Diesel and gas float on water. Water molecules bond with each other (we’ve all seen the effect of surface tension) and droplets have a tendency to bead and collect. Moisture settling out can result in a layer of water under the gas or diesel in boat fuel tanks, and this can get sucked into the engine’s fuel intake. Under diesel it can readily become a breeding ground for microbial spores, commonly referred to as diesel algae or “crud.” (That’s my scientific word for the day.)

Ethanol in gas can greatly exacerbate the water problem. The government is forcing the sale of E10 at gas docks. Simply put, this is gas that supposedly contains 10 percent ethanol, a form of alcohol. Adding ethanol, according to the government, does various good things, like lowering the flash point and saving petroleum usage. (It also helps the flash point of certain congressional pork barrel projects, but they don’t mention that.)

However, ethanol absorbs water, and the mixture of water and alcohol can drop out of the fuel, causing a layer of sludge to form at or near the bottom of the tank. This is sometimes referred to as phase separation. This mixture may be sucked into the fuel pickup line and cause other problems. This may not be a problem with cars and trucks, which refill frequently and aren’t on the water, but it can be a serious problem with boats. And ethanol is so unstable that it’s not stored in gasoline supply tanks — like you and I must do in our boats — it’s added to the gasoline at the distribution point.

7. Most of us have some algae in our fuel from various sources. Even if you carefully maintain your tank and its contents, you often can’t be sure about the storage tanks upstream of your fill hose. And if the fuel is floating on a layer of water or water and alcohol near the bottom of your tank, bacteria and algae will proliferate there, growing more rapidly in warmer temperatures. Even in cooler climes, the fuel in the tank is gradually warmed as it returns from the engine via the return line.

8. Algae does more than just hang out in your tank; it causes other contaminants, such as a slimy, black mass (a little like tar) in diesel that can clog filters and settle down to the bottom, eventually forming a mat. When this mat breaks loose, as when operating in rough conditions, it can clog the fuel line intake, filters and worse.

I’ll never forget the first time I cleaned the inside of my 300-gallon fuel tank on an earlier boat. It was after years of hanging out in the Bahamas. Having seen things like I described at the beginning of this article, I’d “invented” my own on-board fuel cleaning system. (This was long before the days when various entities had lined up to sell their great ideas for on-board fuel polishing, which are similar to what I did then.) In horror, I pulled the stuff out in sheets as it remained sucked against the end of the intake hose for my fuel tank vacuum.

9. Cetane and octane ratings are an area of concern. Without going into a scientific dissertation, these numbers — in different ways for diesel and gas — have an impact on how well your engine runs and its efficiency. Poor ratings also mean more waste product from the engine — in other words, more pollution. Interestingly, the changes being made to fuel to allegedly protect the environment (ethanol and reduced sulfur) can work to lower those ratings. On many new gas and diesel engines, for example, computer control will alter the engine’s firing rate as the octane or cetane number lowers.

10. Ethanol also has been linked to the deterioration of fiberglass tanks, particularly older tanks. This can weaken tanks and cause gasoline to leak into the bilge, where it could lead to an explosion and fire. The substance leached out of the tank can plug filters, and there have been many reports of it passing through filters and causing deposits that permanently damage engines. (See the Seaworthy section of the BoatU.S. Web site ( ) for results of independent lab testing on the subject.)

Some sources, particularly those in the Midwest where E10 has been in use for years, say ethanol problems simply aren’t that serious unless you have one of the older fiberglass tanks. However, there is significant empirical evidence, from the New England area in particular, that the problems do exist. None of the experts with whom we talked say that fuel additives can help with the problem of old fiberglass gas tanks.

11. Looming over the horizon is the talk of increasing the ethanol content in gas. Some wise souls are even talking about adding it to diesel, apparently unconcerned with all the problems mentioned above and with the fact that it would significantly lower its flash point, thus making a relatively safe fuel very explosive and dangerous. Experts say that the official minimum flash points (according to ASTM specifications) are 125.6 F for No. 2 diesel, 100 F for No. 1 diesel, and 55.4 F for ethanol. They note that when ethanol is added, the flash point drop is not linear and that the addition of ethanol would cause a significant and dangerous lowering of the flash point.

12. Biodiesel can create issues. Experts say it causes some of the same problems as ultralow sulfur diesel, including poor stability and susceptibility to bacteria growth. Biodiesel also contains about 3 percent less BTU (energy content) than diesel fuel, which causes somewhat reduced power and increased fuel consumption. It can be made from various raw materials, and a byproduct is glycerin, which if not filtered out can cause various problems, such as filter plugging.

13. When we fill up and shell out, there are many things we may not know about the fuel we’re adding, like the actual cetane or octane numbers, how much water it contains, or the micron rating of the filters on the pump or when the filter was last changed. We might not even know if we’re pumping E10 or a higher blend, because somebody might have goofed when they added the ethanol at the distribution point. If we’re pumping diesel, we might not know the actual sulfur content. And when we think we’re getting the good old stuff (supposedly still available in some areas, particularly along the southeastern coast) we may actually be getting gas with ethanol or low sulfur diesel.

14. Bad fuel on a boat doesn’t mean simply coasting over to the side of the road and waiting for AAA after the engine stalls. Sure, the government is supposed to be looking out for us as it stands like the witches of Macbeth over its boiling pot of mandated fuel mixtures, but do you trust that? Speaking only for myself, I don’t. These were the people who, to help the environment, mandated the addition of MTBE to gasoline, which they now say is such an environmental threat. Ethanol is the replacement for that.

And there’s another very real issue: If I’m coming into an inlet with seas breaking all around and my engine shuts down because of changes to the fuel, the fact that some intellectual in an air-conditioned cubicle or fat cat behind a pork barrel desk in D.C. says it’s OK isn’t going to help me a bit. And I suspect that my boat breaking up in the surf isn’t going to be all that great for the environment.

Is there a doctor in the house?

Are you feeling good about all this? I’m not. But I believe there are helpful additives available; it’s not all about side shows and snake oil. There’s big money in the additive business, lots of competition and plenty of customers. Many of them, especially boaters, pay close attention to what they put in their tanks and whether it performs as claimed. A vocal, knowledgeable and involved consumer base should benefit the marine community.

But even though competition among additive makers is strong, there isn’t the regulatory oversight regarding advertising claims as there is, for example, over what we eat, the medicines we take and the cars we drive. If one thing is clear, it’s that you and I should make our choices carefully.

In an attempt to gain better insight, I interviewed experts from five well-known companies about the issues and solutions. I wasn’t surprised that there was disagreement in various areas, including, of course, which products are best. Obviously, these people recommend their own products, but what they told me can be helpful in investigating products and deciding what’s best for you.

What can I do?

If you’re like me you’re thinking, What can I do to make wise choices?

1. Consider your issues. Do you burn diesel or gas? Are you experiencing excessive smoking or knocking? Are your filters getting dirty quicker than usual, or is there an unusual amount of water showing up in them? Is there a grayish-white substance on your filter (possibly sludge from phase separation caused by E10)? If you have a diesel, do you see excessive black particles on your filter elements or deposits on the sides of your tank, particularly near the bottom? Are you sure about the fuel you’re putting in the tank?

2. Keep a log of your observations and include such items as changes in exhaust or efficiency, smoother or rougher running and filter conditions.

3. Don’t hesitate to call additive manufacturers and ask them difficult questions about your symptoms and their products.

4. Consider the company behind the product. If it’s a solid, reputable company that’s been around awhile, its claims are more likely to be valid.

5. Look in company literature (often found on company Web sites) for third-party tests that validate claims. The American Society for Testing and Materials (now international) develops standards for conducting meaningful and valid testing. There also is the American National Standards Institute and other independent organizations, such as the National Association of Corrosion Engineers, that develop standards for testing. If applicable, check whether the tests cited to support product claims were conducted according to standards of these or other recognized standards-setting organizations. If they were, the manufacturer usually will state as much.

6. Check the Material Safety Data Sheet for the product. These are required by law for most chemicals and substances that could be dangerous to those occupationally involved with the products and emergency personnel. Many major manufacturers post the MSDS for their products on their Web sites. Failure to have these for products that require them (fuel additives normally would) could result in serious fines by the Occupational Safety and Health Administration. Although MSDS aren’t normally intended for consumers, they do contain information (such as ingredients) that may be helpful to you. (To learn more about MSDS go to , and select from the drop down menu next to “Web advertising.”)

7. Don’t expect miracles. Look for reasons for a product’s alleged performance. Ask yourself or a product representative, “Exactly how does it do this?”

8. Ask for recommendations from informed, mechanically oriented friends or professionals, but remember that this is an area rife with biases, personal interest and lack of knowledge.

9. Use only additives approved by your engine manufacturer.

10. Regardless of the additives you choose, have your tank professionally cleaned when needed, pay close attention to your filter elements (a vacuum gauge helps with this), and be very careful about the fuel you take on.

11. If you’re at a questionable diesel fuel dock, put a little of the diesel in a small glass jar before filling your tank and look for impurities. If you think the fuel is suspect, use a filter like Racor’s RFF15C. Follow the instructions carefully, including those about proper grounding to avoid explosion.

12. There have been several articles on the subject in Soundings. Search the story archives at Keyword: ethanol.


The issue of having good fuel that works well in your engine and truly helps the environment will continue to evolve. Sorting fact from fiction, especially with all the fiction coming from Washington, will probably continue to be a challenge. Additives have played a role in the care and feeding of engines for a long time. My guess is that their role will become even more significant as the government, in order to help the environment, continues to formulate fuel for the masses (road vehicles) based on sometimes questionable science and without due regard to more unique users, such as boats.

Tom Neale is technical editor for Soundings and lives aboard a Gulfstar 53 motorsailer. You can buy his book, “All in the Same Boat,” at .