Under Seat Fuel Tank Sending Unit Question

Hi all,

So.. I ordered a new sending unit for my under-seat tank. Here is where I am a tad bit confused. I assumed the vent tube would be the smaller diameter tube however when I look at the sending unit, the smaller tube appears to be the feed? The larger tube goes up towards the top of the tank so I am assuming this must be the vent.

Thanks!

 

Don't know what model you're working on...
Sounds more like the main feed line and a fuel return line back to the tank.

 

I'll try and get a picture.. I think it will make more sense..

 

Two tubes in, two tubes out ?
Should be main fuel tank feed line and the fuel return line.
Larger diameter tube would be main fuel tank feed and smaller diameter tube would be fuel return line.
Of course, your fuel pump and/or fuel filter must have the return line feature/function.

 

Correct.. Let me see if I can clarify.. I will try and get a picture on my lunch break today..

At the fuel pump (I am clear on this):
-Small tube is for vent.
-Large tube is for feed from tank
-large threaded hole feed to carb

At the sending unit in tank (This is where I need a bit of clarification):
-Large tube (Originally I thought this was for the feed to the pump but this runs to the inside top of the tank... so it must be vent)
-Slightly smaller tube (very short terminates at bottom of tank, must be the pump feed line?)

The reason I am confused is I assumed that the feed from the sending unit (tank) would be the larger diameter. The smaller tube is not nearly as tiny as the small tube at the pump but it is the smaller of the two, and it terminates at the bottom of the tank...

 

Ok, Here is a pic... If you notice the smaller diameter tube terminates at the lowest point, so this must be the connection to the main input on the fuel pump right? The larger one runs to the top of the tank via that long tube... must be the vent connection??

 

I thought this too, but the current under seat tank has the sending unit on the bottom...

 

It looks like you guys are right... The prior owner(s) must of done some weird Jerry-rigging. Looks like I will replace the tank. does anyone have pics of how their fuel lines run from the tank through the tub?

 

Your tank is inside the tub with you?

And are you confusing the sending unit with the fuel pickup?
The F-Head underseat tank fuel outlet is at the center of the bottom of the tank. There is a hole in the floor there for the outlet fitting and the fuel line runs inside the side rail up close to the fuel pump where a flexible tube picks up the distance between the end of the fuel line and the fuel pump. There is a second hole close to that one that is for draining the tank. The sending unit goes into the top of the tank which is where the electrical connection between the sending unit and the fuel gauge is made.
Turn that sending unit upside down from the picture and that is how it will go into an under the rear gas tank. Holding it in the right orientation, the long tube goes down to the bottom of the tank for fuel pickup, and the shorter tube goes to either a vent or the return line from the fuel pump (this is most likely).

 

The OP has a V6, the feed and return lines go into the top of the tank.
The lines come through a hole in the floor next to the tank, near the center of the vehicle, and curve up over the top of the tank to the sending unit.
This picture is looking straight down between my seats.

 

Interesting. Most of us would mount that under the rear floor between the frame rails. Or if it is the right size and shape, under the passenger seat in place of the tool box. The PO was single, wasn't he?

 

Thanks for that pic, that will help me route my lines.. Looks like I am going to have to fab up a patch panel to plug this hole someone cut for their inverted sending unit lol.

 

Yup single tank...