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Is it OK to drop fuel line diameter?

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Beany_bot

Member
For a few reasons (changing tanks) I would like to drop my fuel line from filter to tank from a 3/8 to a 5/16.
Would this cause any problems with fuel delivery?
 
Im doing away with my inboard tank as I don't trust it (number of reasons). Id rather not rip up the floor though so It's staying in the boat and shall be made safe. I will be using two 30lt plastic tanks at the back of the boat but every single aux tank I find has a barb for a 5/16th fuel hose. I cant even find suitable replacement barbs to take it up to 3/8th. So looks like I will need to run a 5/16th fuel line. That is, if it will be fine to do so.
 
It would help if you were to tell us which boat model and engine this fuel supply is for.


Personally, I'd do the work, and would replace/repair the original fuel tank.
Having the capacity and the weight placement where it now is, would be a real plus!

It will also not dimensish the boat's value... if that's a concern!


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It's a sunbird corsair 218. Running a 1991 5.7 OMC cobra. I'm planning to use the existing tank as a ballast tank for wakeboarding. I really don't want fuel down there.
 
Basically all Im asking is will the 5.7 V8 be able to draw enough fuel through a 5/16th line as apposed to the usual 3/8th line. (10mm vs 8mm)
Thanks.
 
kimcrwbr1 said:
You should be able to get 3/8 barbed nipple fittings at most any hardware store but 60 liters is only 15 gallons of fuel, your not gonna get alot of time on the water between fill ups?
Click to expand...

I've tried and tried. None of them fit the tanks. That would be the ideal solution. But im in the UK, hard to get these things.

60 Litres a day is plenty for what I do. 60 Litres is $133 here!
 
agree on fixing or replacing the original tank...i was forced to go the way he is going with two 6 gallon tanks...i am running an aluminum bass boat and the boat was literally built around the tank...the tanks are a pain in the butt and take up room...and its amazing what a few extra gallons will make in range..i carry a 2.5 gas can just to be safe...and i am only running a 60 hp 4 cycle efi..there is another problem with running two tanks..you have to switch tanks after 6 gallons...and if you are going to make a run that you know will run one tank dry because it is low then what do you do?...if you are running in weekend or barge traffic running out of gas can be unsafe...you could put a valve in to switch but that either ends up with more hoses in the boat or limits where you can place the tanks..a royal pain in the butt..
 
Im sorry for repeating myself but can anyone tell me. Will the 5.7 V8 be able to draw enough fuel through a 5/16th line as apposed to the usual 3/8th line. (10mm vs 8mm)
Thanks.

Just to confirm once more...

- I want to use my existing tank as a wakeboard ballast water tank.
- I want to use auxiliary tanks as fuel theft is a problem in my area. And I can take these away to fill them.
- I want to use auxiliary tanks as I have an outboard boat too and they can share tanks.
- I wont burn more than 40 liters a day.
- I don't want to rip the boat apart, as, you can see above. I don't need to.

 
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It's your boat.... do what you want to!
However, as you can see...... some of us are recommending that you replace or repair the OEM fuel tank.
Some of us perhaps have a good idea as to what this may do the characteristics of your hull.

************

As for your main question...... going from 3/8" fuel line down to 5/16" fuel line.... this will create a bit more resistance.
Resistance = reduced flow.
Also, length will be a resistance factor.
You may experience some velocity increase given that the fuel pump suction is adequate.

I'll assume that for good reason.... the OEM determined that 3/8" fuel line was appropriate for this engine.

Again.... it's your boat.... do what you want to!




Food for thought.
Some will keep asking the same question until they get the answer that they've been wanting to hear all along.
If what they are hearing repeatedly makes any sense... perhaps it's valid!


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