Small dripping diesel leak near copper outlet valve

[Menlim3]

I have a diesel tank with a short (5 cm long) copper tube (7mm diameter maybe) sticking out of the low point. Then there is an on-off valve. Then more copper tube leading to the engine. I think the leak is at the connection between the copper tube and the valve (closer to the tank) since when I close the valve the leak continues. Is this the right diagnosis? Next, can I fix this without first emptying out the tank? I know I"ll probably need a special "coning" tool for the copper connections. Or maybe not? Can someone walk me thru the steps please? Thanks!

[model 10]

You say it still leaks with the valve turned off? If you have to remove the valve, have a plug ready, It can be done but I would drain the tank personally. I hate that smell inside the boat.

[Menlim3]

Originally Posted by Guy

You say it still leaks with the valve turned off? If you have to remove the valve, have a plug ready, It can be done but I would drain the tank personally. I hate that smell inside the boat.

yes. it still leaks when valve is turned off.

[Captsteve53]

Once you make the repair consider this below fuel line requirement for copper fuel lines ABYC:

A loop of copper tubing or a short length of flexible hose must be installed in the fuel supply line at or near the engines. The flexible hose must meet the requirements of .ABYC H-33

I know this dosent fix your present problem but it may prevent a recurring or new problem,perhaps if you dont have this presently it could be a part of your repair

Cheers Steve

[Uncle Bob]

Originally Posted by Menlim3

I have a diesel tank with a short (5 cm long) copper tube (7mm diameter maybe) sticking out of the low point. Then there is an on-off valve. Then more copper tube leading to the engine. I think the leak is at the connection between the copper tube and the valve (closer to the tank) since when I close the valve the leak continues. Is this the right diagnosis? Next, can I fix this without first emptying out the tank? I know I"ll probably need a special "coning" tool for the copper connections. Or maybe not? Can someone walk me thru the steps please? Thanks!

Yes you do need to empty the tank, because you need to repair the connection between the valve and tank. This will require the removal of the valve, identification of the source of the leak, correction of the problem and reinstalling the valve and line.
For what it is worth I would, if possible, install the valve directly to the tank which would allow you to work on the fuel line in the future without any problems.
Cheers

[TrentePieds]

Solid copper tubing throughout the run from tank to engine is an invitation to problems. Best bite the bullet and do it right! Depending on just where the fracture of the line is twixt tank and valve, that might require the removal of the tank.

The "best practice" for tank design is to take the outlet through the TOP of the tank. That obviously means that the fuel has to be taken from the tank by suction rather than by gravity. The pay-off is that the tank cannot dump it's contents into the bilge due to a broken outlet.

The engine will have a "transfer pump" that provides the vacuum to suck up the fuel and deliver it to the fuel filter(s). A separate transfer pump is also sometimes used.

Even when set up in this manner, there should be a flexible section in the line to absorb the vibration cause by the engine. In the old days a section of coiled tubing was used. These days a section of plastic hose is more common.

I assume that your tank is metal. If so, I do not see that a satisfactory repair can be effected in situ.

TP

[jamhass]

IF the leak is far enough away from the tank that you end up with an inch or so of good copper tube, you can use a compression or swagelock style valve or tubing. Although messy, this could be done without emptying the tank. Takes some forethought, but usually doable.

[Compass790]

Clean the area then wrap toilet paper around the pipe btwn tank & valve. See which end gets damp first. If leak is there you will have to drain tank. Have you tried tightening the fitting? I've had good success with thread tape on flared or coned fittings but only use that BEFORE the fuel filter. Injection pumps dont like thread tape. (Dont ask me how I know) If it's cracked see rubber fuel line suggestions above

[Cheechako]

Sounds like a bit of a problem. Bottom draining tanks went out decades ago. I'm having a hard time visualizing the whole setup, but is the tank threaded? it would be nice to eliminate that tubing and mount the valve right to the tank. Have you tried just tightening the connection between the tube and the valve? Often that stops flare or compression fitting leaks. With rigid tubing all the way to the engine, vibration may have loosened it just enough.
Beware when tightening fitting on copper tubing, you need to hold both the tubing fitting and the valve with a wrench.

[Tia Bu]

I had exactly that problem on an older Jeanneau. To complicate matters, the tubing and old valve were metric, and I couldn't find replacements in the U.S. The solution turned out to be fairly easy: I cut out about 8" of tubing around the valve, then replaced it with two short pieces of flex tubing on either side of a new valve. I did have to empty the tank, and then I had to have a bucket ready to catch a bit more fuel when I cut the old line.

[Rorzech]

Oil code forbids the use of teflon tape and compression fittings. There are reasons for these codes. Teflon tape on flared connections ? BTW engine vibration "work harden's" soft copper tubing making it brittle before it cracks. Use a flexible fuel hose to connect to the engine.

[davil]

for whatever value has my opinion I personally will think twice before tightening any thing,afraid will "open the gates of hell"
Usually in my experience the difference between good enough or livable and perfect is a cracking sound.

good luck

[sandy stone]

Originally Posted by Rorzech

Oil code forbids the use of teflon tape and compression fittings.

What code is that? Not familiar with it.

[David M]

Originally Posted by sandy stone

What code is that? Not familiar with it.

You don't use Teflon tape nor compression fittings for Diesel lines. They can leak very easily. This is not allowed on USCG inspected passenger vessels either.

Flare fittings, JIC fittings and liquid gasket material rated for Diesel is allowed.

https://www.permatex.com/products/ga...ealant-liquid/

[Compass790]

I couldn't care what USCG thinks. I'm only interested in what works & thread tape does.