Fuel tank sending unit

I see three fuel lines going to my sending unit. What is the third one? There'd be fuel from the tank, fuel back to the tank, and ?? Maybe vent? But where does the line go, since there's no charcoal cannister or anything like that?


Not urgent, I'm just curious and I haven't taken the time to trace the lines.

the third is just a line that pops out right behind the rear cab frame crossmember and points straight down, it has a little rubber boot on the end to plug it off. my guess is to drain the tank!!

Yeah, I just noticed that. I've got the tank off for replacement and here's this stray fuel line just blocked off 4" from the sending unit. I'm glad to hear that it's that way on yours too and not just some hack job from the previous owner!

That line may also be used by the arctic kit with the fuel burning swingfire heater. My M1009 had a plugged tee on one line going to the fuel pump but the 1008 might be different. Just a thought!

So I found this thread a little after I found a huge puddle of diesel on the asphalt.

What is this line and why does it have fuel coming out of it. Seemingly spontaneous.
Maybe related: filled it up a few days ago.

Tossed a quick fix on it but can this be capped permanently?

I believe that is the fuel tank drain line, and is supposed to have a cap on it.

Thank you. This truck has given me a few surprises.

I'd suggest taking a look at the TMs. At least the -20p and -34p to see exploded parts diagrams.

Those are very difficult to use on the phone. I have been trying periodically.

Obijuank5 said:

So I found this thread a little after I found a huge puddle of diesel on the asphalt.

What is this line and why does it have fuel coming out of it. Seemingly spontaneous.
Maybe related: filled it up a few days ago.

Click to expand...

Didnt the 11 year old thread already answer your question?
Very clear to me on what and where it was. And you plugged your line in that exact same location.

No flame intended. Just wondering why you asked what was already answered.

If I missed something I apologize

No. I interpreted it as a very vague "maybe not sure"
Individual results may vary i suppose.

Hmm, interesting to see this, I changed mine a few months ago and the replacement from LMC only had 2, I assumed the 3rd was because a gasoline sending unit was used as a fix sometime back as the evidence pointed to the tank being replaced in the past. I figured for gasoline their would be a emission canister it hooked to. The LMC one sucks if anyone was wondering it basically has the float misaligned so at empty you have 5 gallons left and it it goes about 25% past full when full. Otherwise, it is better than perpetually full which is what I had.

The TMs show that line drain and tells what year they stopped extending it towards the tire.
83-84 I think
Not Sure

When I replaced my sending unit years ago I remember it being an additional feed but it does not go the to the bottom of the tank. So yes, you could run a fuel fired heater or drain most of the tank using this line. My unit just had a rubber cap on the sending unit metal line on top of the tank.