Could you connect two diesel tanks like this?

[cmedsailor]

I hope this is not a stupid question but I prefer to ask something stupid rather than do something stupid. As it seems to be enough space on a lazaretto to fit a second plastic fuel tank (around 40 litres probably – not the biggest but still an improvement to the very small 75 litre tank of the boat) is it a good idea to connect it above the original tank and simply have a valve to let the fuel flow to the original. A kind of “permanent jerry can transfer” you could say, just easier when things get tough. What worries me though are these black residues that will be created at the bottom of the second tank (similar to having diesel in a jerry tank for a couple of weeks) that will flow to the original during transferring

 

[Juggler7823]

Depending on the height of the upper tank and the amount of fuel in the bottom tank, it could overflow through the bottom tank breather pipe.

 

[PCUK]

There shouldn't be any black residue however you store diesel.
The best plan would be to have the tank at the same level so that when you open the cock the fuel finds it's own level between both tanks and won't cause the overflow mentioned above.

 

[whipper_snapper]

If you are going to do that, why not reverse it and use the upper tank as the 'day' tank to send fuel to the engine and which you replenish by pumping fuel up from the old, lower tank. That gives you several advantages including a system more tolerant of small air leaks because it is above the engine and the ability to keep the two tanks separate if necessary rather than having to always run the top tank through the lower.

 

[castaway]

I can't see any reason why not.

I have 2 x 50 gallon tanks each side of my engine compartment and they are linked by a 'balance pipe' between the two.

In reality I run on only the stbd tank but if I want to use fuel from the port tank I just turn on the tap and let it transfer.

I found early on in my ownership not to leave the transfer tap turned on whilst sailing as the one or the other is likely to over flow dependant on which tack.

Cant see and virtue on having a day tank and having to pump fuel up to it.

Regds Nick

 

[Athene V30]

Sounds about the arrangement I have.

8 gallon 'day'tank above engine and flexible tank (25 litres i think but never measured it, really ough to sometime) in starboard locker and pump between.

BTW 8 gallons is about 24 hours running under power so I guess it really is a day tank!

Works fine. Never got anywhere near running out in day tank.

 

[boatmike]

That's a good arrangement in itself and fairly standard on larger vessels. You could improve it further by fitting a racor filter or similar in the supply line downstream of the delivery pump between the two tanks and having a return line with a valve in it to drain it back when you want to. This then means you can periodically empty the day tank to clean it and always ensure that clean fuel is held in the day tank.