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fuel tank level issues while running

Discussion in 'Ocean Yacht' started by Anthony Kaduk, Sep 23, 2018.

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  1. Anthony Kaduk

    Anthony Kaduk New Member

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    I have noticed a strange condition with my fuel tanks and feeds while running and am wondering if anyone has seen similar conditions.

    I have a 2002 52SS. It has 5 fuel tanks: 2 saddle tanks and 3 under floor tanks. The two tanks on each side are connected in series to the center floor tank (the port saddle feeds the port under floor which feeds the center under floor; same for stbd.). Fuel passes from the center under floor tank to a manifold that feeds the engines and generator. There are two fuel gages: the port gage measures fuel on one of the saddle tanks; the stbd. gage measures fuel in the center under floor tank. If all tanks are full and I run for say 4 hours I have noticed that the saddle tank level will drop as expected but the center under floor tank drops also. If I stop for overnight, the next day the saddle tank level will be lower and the center under floor gage will read full. Seems that as I am running the center tank does not fill as fast as the fuel is drawn out. Longest time I have run is 7 hours and I have never had a problem with running out of fuel but I have concluded that it would be possible to run out of fuel in the center tank and still have fuel in the saddle and under floor side tank.

    Has anyone encountered anything similar?
  2. Capt J

    Capt J Senior Member

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    Your fuel vents are blocked which isn’t allowing the saddles to drain as fast as the engines are sucking it because they’re under Vaccuum
  3. Anthony Kaduk

    Anthony Kaduk New Member

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    Ran compressed air into the fuel fill and air came out the vents. Slightly more on one side than the other but a good flow of air on both sides. Putting the boat away for the winter but next spring I will experiment with the fuel caps off and see if there is a difference (has to be a very nice day of course. Thanks for the response.
  4. Boomer

    Boomer Senior Member

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    Ever figure out your issue? There could be algae and crud stuck in the hose fitting at the tank
  5. Anthony Kaduk

    Anthony Kaduk New Member

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    Have to wait until spring. Boat is stored in Michigan. Will post final result when I have it figured out.
  6. Capt Ralph

    Capt Ralph Senior Member

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    Where are your return lines returning to?
  7. Anthony Kaduk

    Anthony Kaduk New Member

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    Return lines go to the saddle tanks. Fuel lines that connect the saddle tanks to the 3 under floor tanks are the same diameter as the fuel line coming from the center floor tank that feeds the manifold that feeds the engines. Therefore there should be no problem with the saddle tanks always keeping the under floor tanks full unless a vacuum is present, eg. vents are clogged, but I had no problem running compressed air thru the fuel fill pipes and out the vent. I plan to run the boat with the fuel caps off (nice day in the spring) and see if this makes a difference.
  8. Capt Ralph

    Capt Ralph Senior Member

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    There's the rub; Side tanks are venting under pressure, where are the lower tank vents? Are they venting under a lil pressure?
    Need only to test with 1 psi and a few cfm. Higher pressures will over come vent restriction globs.
  9. Anthony Kaduk

    Anthony Kaduk New Member

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    I don’t think there are separate vents for the lower tanks; just vents port and starboard off the top of the big saddle tanks. Since the tanks are interconnected one vent per side should suffice I would think. If there were vent lines from the lower tanks they would be full of fuel up to the level of fuel in the saddle tanks.
  10. Capt J

    Capt J Senior Member

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    Yes, this is how the fuel tank arrangement works on an Ocean. The saddle tanks gravity feed into the lower tanks, but the lower tanks don't have a vent, they vent from/through the saddle tanks like a culligan 5 gallon water machine. I have seen where if one of the vents is clogged in the saddle tanks, that the tank with the open vent will drain much faster than the other tank. Then once at the dock and over time, they'll equalize back to being even.
  11. Tom Mullany

    Tom Mullany New Member

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    Yes. I have a 2000 56 Ocean. Running the boat North from Charleston at cruising speed the Port tank went down by about 1/4 tank every two hours. I either had to stop to give the center tank a chance to fill or back down to 1800 RPM to keep it from going to E.
  12. cleanslate

    cleanslate Senior Member

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    Can't you run another vent off of both saddle tanks ? To help speed things up? Not the best design by Ocean it sounds like. Most fuel tanks have spare threaded top fittings in them with plugs, for the boat builder to choose from when installing the various motors and such. I would run another vent off your port and starboard fuel tanks and see if that doesn't help. You could rig up a trial run set up to see if it helps before you drill and real vent tube through the hull etc...
    Last edited: Jun 18, 2019
  13. cleanslate

    cleanslate Senior Member

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    That too, is most likely slowing things down....All works well when brand new and clean, then the crud sets in over time....ugh. You may have to get all tanks low on fuel and blow air through all the fuel lines running to and from the tanks, hopefully not back into to the tank where you can where you can get it into a bucket , and get the crud out of the lines and tank fittings.
  14. onyx

    onyx New Member

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    I have a 2001 48 and also experience an issue. After running for a couple of hours I get a slight list to stbd. My gen returns to the stbd saddle tank. I believe it may be a venting issue or it is the returned fuel from the gen.
  15. Anthony Kaduk

    Anthony Kaduk New Member

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    I am not sure how the tanks are set up on a 48. My previous boat was a 45 with just saddle tanks that were dedicated to each engine. In this set up if there was a change in ship attitude I would consider the possibility of one of the engines consuming a lot more fuel than the other if the boat started to list while running. If it was a long run my generator was fueled by my starboard tank and that side always took more fuel.

    I still do not have an answer for mine. If I run for 4 hours both the saddle tanks and the center tank drop. I have taken the fuel caps off of both sides and the center tank does not seem to fill any quicker so I don’t believe I have a vent issue. I have no gunk in the fuel filters or canister to indicate clogging in the fuel lines and since I have owned the boat (2 years) never any water in the fuel filter. I think I could probably run at least 12 hours at cruise (24 knots) before I emptied the center tank so I am not going to worry about it any more.
  16. onyx

    onyx New Member

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    The 2001 48 has two saddle tanks that feed to a belly tank. I have S60's DDEC and the fuel burn is consistent for both. I believe it is the gen fuel return. I agree, these things can drive you crazy and 12 hours is a good run.