68 to 72 Gas Tank swap... what is required?

[crakarjax]

I have a nice '72 gas tank (w/ EEC) and a horrible tank in my '68. I want to swap them and I have removed and cleaned up the '72 tank but the sender is shot. The sender on the '68 had been replaced so it works well, and I'm planning on using that.

I have a couple of questions though...

- Why does the '72 sender have two lines coming out of it, and what improvement is that over the '68 design?

- There is a "vapor line" on the passenger side of the '72 tank. Can I just plug that off or should I try to make it functional?

- Do I need to get a '72 style fuel filler grommet and ditch my '68, and who makes the most durable grommet?

- Where can I get a replacement sending unit filter sock thingy?

TIA!

[crakarjax]

ttt

[Ed 72 Sierra Grande]

Good Question. I have a bad sending unit in my tank and need to get it fixed.

Any help is appreciated.

[crakarjax]

Well, I measured the pickup tube, it is 3/8"... so a 3/8" filter should work. I saw some at http://www.truckandcarshop.com/6072.html for $9, but a new sending unit is only $24 so it would probably be worth it just to replace the whole thing.

I did some comparison of the sending units, and the main difference seems to be that the '72 has an extra outlet the only extends a couple of inches into the gas tank. I can't tell by my catalogs where this line actually goes, but I am certain that it could just be plugged off with no ill effects. In that sense, it may be more "future proof" to get a 72 style sending unit and cap it off in case I want to add whatever that is for in the future.

[crakarjax]

I'm going to go with the 68-style sender, but out of curiosity does anyone know what the difference is between the manual trans and auto trans senders for '72?

[Ed 72 Sierra Grande]

Originally Posted by crakarjax

I'm going to go with the 68-style sender, but out of curiosity does anyone know what the difference is between the manual trans and auto trans senders for '72?

Good question.

[stich626]

the extra line on the 72 is to the charcoal can.. I'd not "just plug it) or you'll get a nice pressurized tank behind you.. and a very dangerous issue when you take the cap off to fill.
the 72 sender with vent to the charcoal can will be a better choice as the "closed system" will afford the gas to last longer.. in the summer heat. it just evaporates, and also todays fuel has ethinol(sp?) in it 10% and they are moving to 15%
it absorbs water an open system (just a vent) will only add to the water being absorbed by the fuel.. and you'll have an issue later as the water sits on top of the fuel in the tank..and builds and builds and, then you have a truck try'n to run on water..
I'd rethink that 68 sender

[w3lfd]

Water sinks to the bottom of the tank, not the top. Water is more dense than gasoline.

Personally, I would use the 68 sender, leave the upper vent hose IF you are using the cap from the 72 tank, and just run it.

[crakarjax]

Why would I get a pressurized tank? The '72 sender with the vent outlet plugged should be functionally identical to the '68 sender, and '68 tanks don't get pressurized, do they?

I do have to use a '72 cap since I have a '72 filler neck. Is the upper vent hose the one that comes off the passenger side of the tank and runs up into the cab corner?

[stich626]

forgot about the upper corner vent..
and water to the bottom.. it was early..
water and steel = rust

[crakarjax]

Originally Posted by stich626

forgot about the upper corner vent..
and water to the bottom.. it was early..
water and steel = rust

So you are saying the 68 sender is better because it has no vent and thus doesn't allow water to be absorbed by the gas?

[stich626]

Originally Posted by crakarjax

So you are saying the 68 sender is better because it has no vent and thus doesn't allow water to be absorbed by the gas?

all I know (as I'd have to dig out my extra tank)
is with todays fuels I'd want a sealed system with a charcoal can
alky evaporates, and absorbs water, when the alky evaporates the water stays and doesn't mix with the gas..
not an issue if you drive it daily, but if it sits..

[Rodk65]

Get the 68 sending unit. Cap off the vent that goes up into the corner and put on a vented gas cap. Everything will vent through the gas cap and you can buy them at carquest and napa.

[crakarjax]

Originally Posted by Rodk65

Get the 68 sending unit. Cap off the vent that goes up into the corner and put on a vented gas cap. Everything will vent through the gas cap and you can buy them at carquest and napa.

Do you by chance know the vehicle application for the vented cap that fits on a '72 tank? I read up on vented/non-vented applications and I think that if I cannot find a vented cap, then I need to run a vent line to a canister to avoid negative pressure in the tank! That means that I'll have to punch a hole in the floor, and I really don't want to do that.

[raycow]

This thread appears to concern the same issue.
http://67-72chevytrucks.com/vboard/s...d.php?t=426566

Ray

[crakarjax]

Originally Posted by raycow

This thread appears to concern the same issue.
http://67-72chevytrucks.com/vboard/s...d.php?t=426566

Ray

Right on, but no real solution was reached, because they don't have the extra hole for the vent line through the floor. I did like the one guy's ide of just ditching the canister and venting under the cab, but without that hole it can't happen, and in that case I might as well search for a vented gas cap which would be equivalent to a vent line right? Well, except for the whole bad-for-the-environment thing...

[crakarjax]

^^ Also, I still haven't heard anyone's take on the '72 vs '68 style fill neck grommet!

[crakarjax]

Originally Posted by crakarjax

^^ Also, I still haven't heard anyone's take on the '72 vs '68 style fill neck grommet!

Finally found someone noting that the 67-70 necks are slightly larger, so I'll be going with the 71-72 style grommet to match the neck.