Diesel spill mystery

February 18, 2012

While I was checking over our 32ft Macwester Malin ketch following a series of storms in January, I discovered what looked like red diesel at the bottom of the engine bay. As it happens, I have never owned or even driven a diesel car, and have had little interaction with diesel until being faced with our Lombardini marine engine. To complicate matters slightly, the anti-freeze that I had pumped into the engine during winterisation last autumn was pink too, so I couldn’t be sure until I got a little closer.

I managed to fit all of the mystery liquid into a 500ml container. It proved to be diesel, with around 50-75ml of water gathering at the bottom of the container. My first concern was that I had some sort of leak from the port fuel tank, which like the starboard fuel tank holds nearly 100 litres of fuel. I cleaned up the spill as best I could and decided to monitor the situation for a few days.

Three weeks later and fortunately no fresh liquid has appeared. Having consulted knowledgeable friends and contacts at our club, forums, and beyond, I’m beginning to think that either:

a) the spill is from an overfill when we brimmed the tanks at Port Edgar just before crane-out.

b) the spill is from the rather choppy force 8 sail that we had returning from filling the tanks up at Port Edgar (on the same day as the overfill).

Of course there are other possibilities, including a leaky pipe or fitting that only comes into play when the engine is running or the hull is moving around. The good news is however that it’s beginning to look as though it’s not a leaky fuel tank, and that was the primary concern that I had.

I’ll just have to keep an eye on it over the coming months, especially during the first week or so after crane-in (which is now less than two months away).



  1. Have you checked to see where the tank vent pipes go, whether they are still attached to the little copper stubs that exit through the vent shields just above the side deck on both sides of your cockpit? Frothing fuel often exits via these pipes to soil your side deck, but would end up in the bilge if a vent was dislodged. Also, I don’t know the Lombardini unit, but there should be a spill line from the high pressure circuit back to a tank, and this is working all the time the fuel pumps are operating (ie for as long as the engine is running). If this is dislodged or leaking at at all, you end up with the same problem. In both cases there would only be a small amount in the bilge, whereas any leaks in tanks or main supply pipes would be both continuous and voluminous.

    Good luck,
    Ted Vary


    • Hello Ted,

      Thanks for your advice and input.

      A member of our club mentioned the vents, but the short answer to your question is no; I haven’t managed to check them yet. It’s on my long list of to-dos prior to crane-in. I hope to get some limbo dancing training in before I give it a go, because there’s not an awful lot of room down there (I was in head-first trying to clean-up the spill).

      Nobody has mentioned the ‘spill line’ from the engine, so I’ll try to check that out at the same time. Thank you : )

      The good news is that the leak doesn’t appear to be ‘in progress’ at the moment, so it seems likely that either nothing more needs done, or there’s a small-scale leak linked to hull movement and/or mechanical movement.

      My gut feeling is that it’s either a simple overfill, or something to do with the vents …because there wasn’t a problem prior to us brimming the tanks and being tossed around on the way back from taking on fuel.

      Thanks again!


  2. Did you ever get it sorted? We had a similar problem on a hired motor cruiser, the smell of diesel being so great as to make the boat virtually uninhabitable. Turned out to be a loose hose pipe clip of the jubilee type at the top of the filler neck so it only leaked when the boat had been recently filled AND heeled. If the two conditions didn’t occur together then it didn’t happen. It heeled for us as we’d taken the bottom as we moored for the night, the full tank allowed the fuel to run back up the filler pipe neck to the loose clip at the top. One screwdriver late – problem solved!



    • Hey Tony,

      Yes …in that we’re managing the problem. It sounds like a very similiar situation to the one you describe. I had been advised that there would be a vent near the top of the system and that if the tanks were brimmed and we were heeled or moving around a lot, the diesel would be spilling out. We’ve managed to prevent further episodes from occurring by avoiding brimming the tanks (something that we had been doing every time we fuelled). That said, I will now ensure that I check the hose & clips assuming that I can get access into it.

      Hope you not only got a hefty discount for your rental, but also charged a fee for essential remedial work!

      Thanks for your input. Happy sailing!


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