Diesel fuel return line

Discussion in 'Diesel Engines' started by johnW, Mar 11, 2007.

  1. johnW
    Joined: Oct 2005
    Posts: 8
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    Location: Hamilton, Ontario

    johnW Junior Member

    A friend's new (to him) boat has the diesel return line connected to the feed line before his first filter. I always thought the return line should go back to the tank(s). Has anyone else piped the return into the engine feed line? Your experience would be appreciated as this would simplify the installation of my Yanmar. My friend's boat has an older 3 cylinder Volvo.
  2. Frosty

    Frosty Previous Member

    Theres 2 types of returns.

    One is a serious amount of fuel and has to return to the tank. Maybe as much as 30 % returns that way.

    The type your friend must have is called basically a leak off return. This a tiny amount and is just what leaks by injectors and pump.

    This can and is normally connected back to the filter.

    My Yanmars even have a fuel cooler before returning to tank.

    This return system where substantial ammounts return to the tank also has the benefit of filtering fuel constantly when on the go.
  3. bilgeboy
    Joined: Dec 2005
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    Location: Boston

    bilgeboy Senior Member

    I didn't know this other style existed, Jack.

    I think if you are installing a new Yanmar, you would want to return it to the tank, at least to have cooler fuel and the constant "polishing" effect Jack mentioned. I don't see this as complicating the massive project you are working on at all. The diesel pick-up and return is the same, doesn't matter how you hook 'em up (at least on my brand new tank). The hose is not very expensive and very flexible.

    Congrats on the new motor!

  4. Frosty

    Frosty Previous Member

    The leak off type is a very small amout I had one once on a big Mitsubushi and I just put the pipe into a plastic bottle . It took weeks to fill it.

    The return should not go to the filter,--I tried it on an initial engine installation, for reasons I can quite fathon out the engine would only run at slow speed. Trying to rev up stopped it.

    Quickly laying in some returns cured the problem imediately.
  5. johnW
    Joined: Oct 2005
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    Location: Hamilton, Ontario

    johnW Junior Member

    Thanks for your advise guys, it was appreciated. This arrangement did not seem like a good system to me but as I have 3 tanks, it would have simplified my installation.
  6. kenJ
    Joined: Jul 2005
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    Location: Williamsburg, VA

    kenJ Senior Member

    3 tanks

    If one of your tanks is considered the feed tank, just route the return to it. In any case I don't think you need to return to all 3 tanks. I don't think the amount of fuel we are bypassing will amount to much, and if it is, you know which tank is getting the partial refill.

  7. Eric Sponberg
    Joined: Dec 2001
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    Location: On board Corroboree

    Eric Sponberg Senior Member

    On the little MD2 two-cylinder Volvo diesel that I had in my 27' sailboat, there was a feed pump with a strainer ahead of it, and between the pump and the injectors was a fuel filter--a large bowl with a paper filter in it. The return line went back to the inlet into this fuel filter. Worked fine on such a small engine.

    On the Moloka'i Strait motoryachts and other large engine installations, we have a day tank that feeds the engines, and any of a number of storage tanks. The return line is usually plumbed to one of the storage tanks, preferrably at the farthest end forward so that the return fuel has a good opportunity to cool before being needed again. If you return to the day tank, the day tank fuel will heat up eventually, particularly if you are on a long voyage.

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