Fuel tank leaks diesel from top, even I have under 10gallons of fuel in it.

[NuDeliTY]

First time writing here, so hello to you all!

So a litte bit of background:
I've got an 1994 Chevy Suburban K2500 6.5td, lots of miles on it but drives still great. Bought it a few years ago to build an overlander. Have been in Norway and around the arctic region with it. Now the truck was standing in my backyard last winter, and about two weeks ago I tryed to fire it up. It didn't, and I found out that there was no diesel in the tank, so i put a little bit fuel in it, bleeded the fuel system, and the truck started, no problem.
Yesterday I went back to perform some kind of springcleaning, and noticed that the grass under the fuel tank is wet. Tried it and it is definitely diesel fuel. Now the fun part begins: There is under 10gallons of fuel in it, and the top of the tank is soaked. It is still dripping fuel, even there is no fuel so hight in the tank. The dripping rate is about one drop every 1-2 second. I haven't started the truck sense two weeks ago. So how can it be it is still leaking, and like I said, from the top.
So can it be that there its a problem with the sender unit? And if so, how can it be that it would be leaking so much fuel even the truck is not running? I took a few pictures for you to look at, hopefully somebody can help to solve that mystery.
It is a littlebit hard to get parts here in Finland, so that's why it would be better to know what to repair before I take everything apart, and trying to find parts here, or somebody willing to send them overseas.

 

[someotherguy]

Welcome,

My guess would be the return line at the sender is leaking. Either loose, or rusted through. Anything is going to be a guess though until you get a good look in there. Kind of tough to see with the tank in place on a Suburban (as you've found) so you may want to go ahead and drop the tank. It's much easier if you siphon the fuel out first.

Richard

 

[CumminsFever]

I suspect the return line as well, but I sure can't explain why it would drain the tank. No matter what, that tank gotta come out. Once it's out, the assessment of the issue can take place. Kinda difficult to diagnose it with the tank in the vehicle.

 

[NuDeliTY]

Thank you, i will start that project as soon as possible, and keep you posted on my findings.

 

[someotherguy]

I suspect the return line as well, but I sure can't explain why it would drain the tank. No matter what, that tank gotta come out. Once it's out, the assessment of the issue can take place. Kinda difficult to diagnose it with the tank in the vehicle.

I didn't read it that it's draining the tank out, just that he's surprised it leaks up top on the tank while the tank is not full (less than 10 gallons) and vehicle is not running.

I'll hypothesize that since the tank is at a lower point than the water separator and other parts of the system up on the engine, that a good amount of fuel could continue to drip out of the return line at the sender since it's downhill from a lot of fuel that might sit in the system after shutdown. Not really a diesel guy so I don't know how accurate that statement could be, though.

Richard

 

[CumminsFever]

I didn't read it that it's draining the tank out, just that he's surprised it leaks up top on the tank while the tank is not full (less than 10 gallons) and vehicle is not running.

I'll hypothesize that since the tank is at a lower point than the water separator and other parts of the system up on the engine, that a good amount of fuel could continue to drip out of the return line at the sender since it's downhill from a lot of fuel that might sit in the system after shutdown. Not really a diesel guy so I don't know how accurate that statement could be, though.

Richard

Well, you make a good point. I mentally added 2 things together. 1st,the fuel tank was surprisingly empty upon sitting for a while, 2nd, it leaks noticeably after sitting overnight or whatever the sitting time was.
I took it that this leak is what emptied the tank in the 1st place. Yup, I may be in the running for idiot of the year award!
Otherwise, you are correct, there is a good amount of fuel being held in the injector pump, fuel filter, and lines. Not less than a quart there.

 

[NuDeliTY]

Well, you make a good point. I mentally added 2 things together. 1st,the fuel tank was surprisingly empty upon sitting for a while, 2nd, it leaks noticeably after sitting overnight or whatever the sitting time was.
I took it that this leak is what emptied the tank in the 1st place. Yup, I may be in the running for idiot of the year award!
Otherwise, you are correct, there is a good amount of fuel being held in the injector pump, fuel filter, and lines. Not less than a quart there.

Hi, an thanks for all the reply’s. The tank is soon out, had to work four night shifts, so that slowed the process.

I considered too that th the fuel would flow from the engine back the return line. But no, it is emptying the tank, the tank is more ore less empty now. I had an bucket where the most amount of drops came down, and there has been dripping about two litres now, in the past 5 days. And the car didn’t run for a few weeks before that.

But i will posting more info when the tank is out.

 

[NuDeliTY]

So, tank is out. Was quite a struggle, there was so much gunk between the frame and the vibration pads that i was very much glued on.

But i found out it was the sender unit, both hoses had rust holes in it. That doesn’t explain the fuel leaking from the top of the tank. I think that by changing the unit, the problem will be solved.

Will be now sanding the rust down and paint it with anti-rust spray, and give it a few layers of some paint. Maybe rubber-comp would be a good option?

 

[CumminsFever]

I avoid using a spray-on rubber compound on surfaces that aren't new metal. The rubber traps moisture under it. Then rust forms. The rubber holds the rust there, creating a growing cancer.
Paint is a good option, or something like fluid-film is my preference.

 

[NuDeliTY]

I avoid using a spray-on rubber compound on surfaces that aren't new metal. The rubber traps moisture under it. Then rust forms. The rubber holds the rust there, creating a growing cancer.
Paint is a good option, or something like fluid-film is my preference.

Good point, thank you. Will doing that.