I noticed yesterday on my 2003 Cummins that I was losing diesel. I just filled up yesterday too. It appears it is coming from the driver's side of the fuel tank. There are some wires that run into the point (mid way on the fuel tank), but it is too close to the frame to do anything about it. It is not leaking from the top. I can see easily the top of the tank. It is not leaking from the fuel lines on top of the tank. Probably have to wait until the diesel is low in the tank to pull the tank, but the question i what is that in the tank were the wires connect? Is it a simple nut that tightens up there or is it molded into that tank?

Thanks
Bob

 

If it is leaking fuel from the top it is probably coming from the fuel line or fuel return line where it connects to the fuel pickup on top of the tank. There are no nuts to tighten. There are quick connects that connect the line to the fuel pickup in the tank. If you do a search for "fuel vent mod", you can find pictures of what the top of the fuel tank looks like and connections.

If you can pull/lift the bed, which is actually easier than pulling the tank, it is very easy to get to and look at/fix. If your truck has ever had the fuel pump replaced with an in tank pump or done the Tank Vent Mod, it could be as simple as a poorly connected fuel line.

 

There are also two small vent ports on the top of the tank where your leak can come from.

 

It is not leaking from the top. I forgot to mention that. It appears to be leaking from the driver's side of the tank where the wires are running to. It is mid-way on the side of the tank and is too close to the frame to really tell, but that is where it appears to be leaking (side of driver's side, mid-way on tank, some sort of electrical connection).

 

The only holes in the tank are on top. If it is leaking on the side, then the tank is bad. I think there is only an electrical connection at the tank if you have an in tank lift pump and that connection goes to the top of the tank. The Fill tube and vent tube are also at the top. The 2003 came stock with the lift pump under the filter, so it sounds like it has been retrofitted after a lift pump issue. Are you the original owner? Has the lift pump been replaced?

I would guess that it may be something simple. When you overfill the tank and a fuel comes out, it goes down the side of the fill tbe/ vent tube and may be dripping onto the side of the tank.

My advice is check the hose clamps on the fill tube/vent tube, make sure the fuel lines/connections aren't leaking. I wish I could be of more help. Savoy also makes a good point. Check those ball valve vents. They may be stuck open.