How important is the vent tube going from the carbon canister back to the fuel tank?

azmusclecar

azmusclecar

Master Mechanic
Feb 13, 2018
439
43
Arizona
I installed a new gas tank AND sending unit...........thought I got the right one but the sending unit only has 2 tubes on it.
One to pump the fuel to the fuel pump and the other is the overflow or return line back to the tank.

I have the carbon canister and I see the line going back to the fuel tank.

Now since there is no 3rd tube in which to hook up the vent line, can I just plug the vent line?

Odd thing is the fuel sending unit has a place to just lay a hose on top of the fuel sending unit and then pinch
the tabs around it.


I ask this now since I now have a fuel leak which seems to be on top of the tank. I thought I did okay with the install but now,
I am getting gasoline deposited on the top of the tank.

I just dropped the tank and cannot find the source of the leak. I installed all new hoses but I am going to redo the entire assembly
since this is not a job I want to do again.

Do I need to get a fuel sending unit for my 1979 Cutlass Calais WITH that 3rd tube going back in to the tank?

Or do you think my leak lies elsewhere.............I'm off the road until this gets fixed sad to say.....

So:

Can i cap off the vent line back to the tank?
Can I use the 2 inlet fuel sending unit or do I need to get the one with 3 inlets?

Thx,
AZ
 
azmusclecar

azmusclecar

Master Mechanic
Feb 13, 2018
439
43
Arizona
69hurstolds

69hurstolds

Royal Smart Person
Jan 2, 2006
2,078
113
You know I'm going to give you the GM part number for the 3 tube sending unit that your car needs. It's GM # 25001613. (You have the equivalent of GM 25001612 at the moment. The last number of the part number in this case tells you the number of tubes)

Dorman part number is 692-089 for the 3 tube version. You can usually find these for about 1/2 the price of the genuine GM parts which have been discontinued, naturally.

I think the Spectra version is FG08A.
 
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spidereyes455

spidereyes455

Master Mechanic
Mar 6, 2013
339
63
Northeastern PA
I may be mistaken but I thought that the 2 line sender was for an application that did not use a fuel return, one line fuel feed to the pump and the second was the vapor line from the charcoal canister. 3/8 fuel feed and 5/16 vapor . If im not mistaken the fuel return on a 3 line sender is 1/4 inch.
 
azmusclecar

azmusclecar

Master Mechanic
Feb 13, 2018
439
43
Arizona
Well the odd thing is, the 2 inlet tube says it is for 1980 as well and I'm not well versed in that years fuel delivery and recovery
system.

I'll just do as suggested and buy the 3 inlet and be done with it. I tried to buy the fuel sending unit that was supposed to
fit my 79 while it was on sale and install it later.

looks like the money I saved will now need to go to the right part.

Live and learn...........thanks for the posts
AZ
 
azmusclecar

azmusclecar

Master Mechanic
Feb 13, 2018
439
43
Arizona
I may be mistaken but I thought that the 2 line sender was for an application that did not use a fuel return, one line fuel feed to the pump and the second was the vapor line from the charcoal canister. 3/8 fuel feed and 5/16 vapor . If im not mistaken the fuel return on a 3 line sender is 1/4 inch.
My fuel pump has 2 lines so one has to be a return line.......and I know I have the right fuel pump so with those two and the vapor line, that makes 3.

I believe you are correct on the hose sizes............very helpful thank you.
 
azmusclecar

azmusclecar

Master Mechanic
Feb 13, 2018
439
43
Arizona
Just to put a period to this issue,

I purchased the 3 INLET sending unit for my Cutlass and glad to report after a test drive, no leaks.
Happy Father's Day to myself..............:banana::banana::banana:

The hose sizes for the inlets as stated by Spidereyes455 were dead on....................THANK YOU!
3/8 fuel feed and 5/16 vapor fuel return on a 3 line sender is 1/4 inch. (y):cool:

new hoses and clamps and this should be good for the rest of my life.

And now for my next trick......................steering shaft replacement................:giggle:
 
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