Fuel tank hose connections

Dr.Jeff

True Classic
On the '79 (carburetor model) fuel tank there are four fuel hose connections (at the level sender apparatus). One feeds the fuel pump (pick-up). One is the fuel return from the carb. And the other two are vent lines. These two are connected by a "tee" just outside of the tank and serve one purpose after that (charcoal canister). Difficult to see everything, but at the bottom of this image there is one hose from the canister (2) to the "T", with a "separator" (3 and 5) on each of the other two ends, then connect to the tank (4).
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I am curious why there are two fuel tank vents that are joined into one hose? Why not just one vent off the tank? Any purpose for the redundant attachments at the tank? I could understand if they had separate functions or connected to different types of SMOG/vapor control devices that must be isolated. But they are not...they simply merge into one hose. Any ideas why?
 
On the tanks I have replaced, there are metal tubes in the tank that go down the left and right side of the tank and attach to those two hoses. However, like you, I have no idea why this was done.
 
I'll look closer at how the tubes are situated when I pull the sending unit to clean out the inside of the tank (waiting for a new seal before separating it). But I think one of those vent tubes is actually part of the tank and the other is part of the sending unit?

Steve, how was the trip to Bangkok? Find any good parts opportunities? Love to hear about it.
 
I noticed a photo in another thread of a '79s fuel lines (below). This one seems a little different that how I recall mine to be. Notice the "Tee" with the two 'separators' (one is hidden behind the left side panel), and here they both go directly to the tank. But on mine it looks like one of these connects to the fuel sender apparatus and the other to the tank directly (I'll have to take another look at mine to see if I'm recalling correctly). Either way, it's the same question...why two vents when one would do?

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metal tubes in the tank that go down the left and right side of the tank and attach to those two hoses
Carl or Steve...Do you know if both of those tubes go the same distance down into the tank? And if they go all the way to the bottom? Thanks
 
Memory suggests they went most if not all the way to the bottom of the tank the same distance. I have never seen a sending unit top piece that would take a vent hose, just the fuel supply (carbed motor) and return supply. Somebody here must have a spare tank laying around they can peek into.
 
Thanks. I was thinking maybe one went all the way down and one only at the top, for different functions of some sort. I also considered the possibility that having two of them was just left over from a prior design, where two different systems needed to be connected to the tank. But I haven't found any such designs noted anywhere. Given the lengths car makers go to in order to save on costs, the redundant vent makes no sense at all. Obviously it doesn't matter, I'm just curious.

Do all X tanks have these two vents, or only certain years?

I'm very likely remembering wrong about one of them connecting at the sending unit, when I get back to it I'll double check.
 
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Thanks. I was thinking maybe one went all the way down and one only at the top, for different functions of some sort. I also considered the possibility that having two of them was just left over from a prior design, where two different systems needed to be connected to the tank. But I haven't found any such designs noted anywhere. Given the lengths car makers go to in order to save on costs, the redundant vent makes no sense at all. Obviously it doesn't matter, I'm just curious.

Do all X tanks have these two vents, or only certain years?

I'm very likely remembering wrong about one of them connecting at the sending unit, when I get back to it I'll double check.

My 87 does. It may have to do with the sloshing that can occur on full tank of gas while cornering.

Paul Davock
 
Just for fun. Here are some pictures of the tank out of my 78X. I can't see any vent tubes running down the sides, but these pictures weren't really an attempt to capture that detail, so I won't claim that they are definitive on the subject.

carb_tank_7.JPG carb_tank_3.JPG carb_tank_4.JPG carb_tank_9.JPG
 
My 1981 has one vent, don’t know was it originally carburetor or FI. And it doesn’t go to bottom for safety in rollover. Tomorrow can post photo how it looks from inside (rusty bottom is cutted off)
 
I can't see any vent tubes running down the sides
And it doesn’t go to bottom for safety in rollover.
Jim, I see the same two vent tubes at the top (outside), but agree they don't seem to run down inside.
Janis, your tank is cut open so no question the vent does not go to the bottom.
Actually for a vent function it would make sense not to go to the bottom, less resistance for air passage if it does not have to draw through the liquid (fuel) first.

Interesting that all years and both induction types all have two vents...in the US. But Janis Euro version only has one. Leads to speculation of Government requirements of some type necessitated the redundant double vent in the US?
 
By the way, I was recalling it incorrectly...both of the little vent tubes at the tank are attached to the tank itself and none to the fuel-level sender apparatus as I suggested earlier.
 
Vent tube confused ???? May stick to original routing. Not sure if to replace vent hoses with new ones or leave well alone at 39 year old black original hoses that are in reasonable condition. May get definitive answer as to where long, dangling vent hos with metal end belongs from charcoal canister.
 
That whole venting arrangement is rather complex and not very efficient in my view. Not sure why there are two vents coming off the tank. Plus all the hoses, separators, check valves, canisters, solenoids, vacuum lines, etc,etc....man it is a lot of crud. I simplified it with one vent from the tank and none of the other stuff.
 
Side hill parking and sloshing. More extreme in a vertical tank. So in either event, one side is always vented.
 
If the vent was located at the top of the tank, like where the fill neck enters, it would work regardless of the angle of the car...unless it is upside down. :p
 
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