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Let’s take a poll… have you ever put gasoline into a diesel tank or vice versa? It happens, a lot. I will confess that I have only made this error once and it was relatively painless as I only got so far as to pump a gallon or so of diesel into one of our gasoline jerry cans. Many others are not so lucky. A friend, who I will not “out” on this blog, recently shared that, for a time, he went by the nickname diesel (admittedly a pretty cool nickname as far as nicknames go), a handle which he earned for filling one of his company’s vehicles with that fuel instead of gasoline. When traveling, errors such as this are pretty easy to make, especially when visiting islands where the language spoken by fuel station attendants is not your native tongue.

  • Note: In French, Diesel is sometimes called Gasoil. Confusing? Possibly.

We are super careful to make sure that when we fill up, it is gasoline that we’re getting and not diesel, even if it means repeating what we want 5 or 6 times. I don’t know what steps are necessary to fix an engine which has been run with the wrong fuel but I can imagine that it’s not a job I’d be too keen to tackle.

On a related subject, certain boats seem to be set up in a way to make a similar and perhaps even more damaging mistake easy to make. They do this by having the deck fill caps for the fuel tank and the water tank (and sometimes the waste tank) side by side. Fortunately, our boat is not like this at all, each of the three being quite removed from one another. We have, however, seen boats where all three caps are directly adjacent to one another! That, in my opinion, is a disaster waiting to happen.

When we were last in one of the chandleries here I noticed that they were selling color-coded deck fill caps to replace the standard stainless steel ones, obviously to help prevent such mistakes. Mistakes which we know do happen. Perhaps certain boat designers should have thought this out ahead of time?


  1. Yep, we did that once . Lucky for us, we only put a few gallons of gas into our diesel tank, otherwise we could’ve killed our engine. Now we ALWAYS check by doing three things: ASKING the attendent “This IS diesel, right?”, smelling it and testing the color before we fill our tanks. Those caps look pretty neat!

  2. Besides being located on opposite ends of the boat from the water and waste caps, our fuel deck fill cap requires a different (size & shape) key tool. What’s more, the diesel tool is bright chrome and the waste & water (they are the same) tool is a grey aluminum. And the water fill is under a hinged, fiberglass cover as opposed to a flat deck fill. So minimal chance for a mistake. BTW, the water and waste tool matches our winch handle shape so we have a backup in the event we drop that specialized tool overboard. The diesel tool is another matter.
    So points to Lagoon on this issue. Apparently they thought about this issue during the design stage.

  3. After filling our 12 gallon diesel tank (single cylinder Yanmar) on a fuel dock somewhere on the inter coastal in NC we headed for the local store. When we returned to cast off, all hell was breaking loose on the dock. The kid had just pumped hundreds of gallons of gas into the diesel tanks of a big power cruiser. The owner of the boat was going ballistic. We just put, putted away, nothing we could do to help, leaving them all in their misery!

  4. While gasoline in a diesel can do some serious damage (it lacks sufficient cetane rating and ignites on the up-stroke), diesel is completely harmless to a gasoline engine. I’ve actually known folks in my marina to use biodiesel in 2-strokes instead of 2-stroke oil (I don’t recommend this–no maker does–but you can Google it. Also remember that biodiesel is a much better lube than diesel.). Too much diesel and the engine simply stops. The cure is simply to drain it out, including the lines.

    I always look to see which pump they are using, no matter if they seem clear.

    Yup, a guy I worked with 30 years ago did this to a large truck (30,000 pounds) that just happened to have a gas engine. He got about 1/2 mile, walked back to the office, and marched straight into his boss, requesting his ass chewing, which by that time the boss was far too amused to deliver. We still remind him of it!

  5. We just docked at a fuel dock in Fort Lauderdale for the very first time. Our only problem was pulling away quickly to make the opening of the 17th street bridge we hit our outboard and dinghy. Ouch! Off for our first shake down cruise.
    All our deck openings are the same so I love the color codes.

  6. Of course, in “English” speaking countries gasoline is petrol, diesel is diesel and gas covers all kinds of gas – LPG, propane, butane, without being specific about it. This adds another dimension to making sure you have the fuel that you want.

  7. On our very first charter, the waste and water plugs were right next to each other, each designated with just a “W.” Yep, when we went to top off the water tank before leaving the dock, we actually filled the holding tank . . .

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