1972 EEC In-Cab Gas Tank Dilemma

[myoldchevytruck]

Below is a diagram of a 1972 EEC Gas Tank. Since the 72 tank is different than the 67-71 (NON EEC), I'm confused about the tank venting. Here's what I know.

There's a vent fitting on the passenger side of the tank

I have a stock charcoal canister and it has an in/out fitting

I have the vent loop tube that goes up to the Passenger Side Pillar (from another truck)

There's a Sending Unit with 2 lines and there's also one available with 1 line


Does anyone know the correct setup. Do I use the Sending Unit with 1 or 2 lines? What is the proper venting for my setup? Do any of these lines go to a vacuum for venting?


BTW, I have a 69' SBC 350/Automatic. Yes, I have a 72 In-Cab Tank. I did not relize it when I got it but thats okay. I have had it boiled clean and sealed.



Thanks in advance.

[myoldchevytruck]

ttt, diagram posted

[myoldchevytruck]

C'mon guys, no-one has a stock 72' in-cab tank setup? Getting close to finally running the truck.

[FormerMember]

You have the proper schematic for the tank there.

If you want to run the later style configuration, that's correct. The earlier style wouldn't have the charcoal canister (AFAIK).

I guess most guys are trying to figure out what the question is?

[Stock72c10]

I have issues with gas smell so I checked out my carbon canister last night (72 C10 straight six). I found that the carbon canister had three lines going to/from it, one went to the carb, one just hangs down towards the ground and is open, the other has been chopped and a screw plugging it (I take it this is the one that goes to the tank). I will be looking further into the correct hookup this weekend to see if I can figure it out. I did notice that in your pic you don't show a hose going to the carb.

[myoldchevytruck]

Originally Posted by grendel

You have the proper schematic for the tank there.

If you want to run the later style configuration, that's correct. The earlier style wouldn't have the charcoal canister (AFAIK).

I guess most guys are trying to figure out what the question is?

grendel, Thanks for the input. I guess my question is, if I use the 72' sending unit - it has 2 lines (one going to the fuel pump and the other going where?) If I use the 67-71 sending unit, my diagram would seem correct for venting purposes. The only other thing for me to do would be to go from the canister to a vacuum (carb or intake) for proper venting.

Originally Posted by Stock72c10

I have issues with gas smell so I checked out my carbon canister last night (72 C10 straight six). I found that the carbon canister had three lines going to/from it, one went to the carb, one just hangs down towards the ground and is open, the other has been chopped and a screw plugging it (I take it this is the one that goes to the tank). I will be looking further into the correct hookup this weekend to see if I can figure it out. I did notice that in your pic you don't show a hose going to the carb.

stock72c10, Thanks for your input also. As far a gas smell, that's what I am trying to eliminate. With the proper venting configuration AND the correct cap (p.s. check your cap because a bad cap is notorious for causing gas smelling in the cab). From what I understand, no line should go to the ground for venting. As far as a line going to the carb or even to the intake, that's what I am trying to figure out. Going to the carb or intake would be connected to a vacuum, ultimately, properly venting the tank. My canister only has 2 lines. Why yours has 3 may be due to different state laws for emissions purposes.

[FormerMember]

Originally Posted by myoldchevytruck

grendel, Thanks for the input. I guess my question is, if I use the 72' sending unit - it has 2 lines (one going to the fuel pump and the other going where?) If I use the 67-71 sending unit, my diagram would seem correct for venting purposes. The only other thing for me to do would be to go from the canister to a vacuum (carb or intake) for proper venting.



stock72c10, Thanks for your input also. As far a gas smell, that's what I am trying to eliminate. With the proper venting configuration AND the correct cap (p.s. check your cap because a bad cap is notorious for causing gas smelling in the cab). From what I understand, no line should go to the ground for venting. As far as a line going to the carb or even to the intake, that's what I am trying to figure out. Going to the carb or intake would be connected to a vacuum, ultimately, properly venting the tank. My canister only has 2 lines. Why yours has 3 may be due to different state laws for emissions purposes.

The other line from the 2 line sending unit goes to the vacuum canister. Vacuum canister can have 2/3 lines. One vapor in from the tank, one overflow out to the ground and the third optional one could be into a vacuum port on the carb.

[myoldchevytruck]

Originally Posted by grendel

The other line from the 2 line sending unit goes to the vacuum canister. Vacuum canister can have 2/3 lines. One vapor in from the tank, one overflow out to the ground and the third optional one could be into a vacuum port on the carb.

Okay, well my canister has 2 ports. I guess the vent on the P/S of the tank and the 2nd line from the sending unit can both go to the canister should I still vent through vacuum. Can I use the 1 line sending unit like in my diagram and have the 2nd port on the canister vent to vacuum? Hey thanks for all of you input, sorry for busting you nuts on these questions. I just want to do the right thing. Thankfully, I live in Florida and emissions testing stopped about 7-8 years ago.

[FormerMember]

Originally Posted by myoldchevytruck

Okay, well my canister has 2 ports. I guess the vent on the P/S of the tank and the 2nd line from the sending unit can both go to the canister should I still vent through vacuum. Can I use the 1 line sending unit like in my diagram and have the 2nd port on the canister vent to vacuum? Hey thanks for all of you input, sorry for busting you nuts on these questions. I just want to do the right thing. Thankfully, I live in Florida and emissions testing stopped about 7-8 years ago.

That would work. Think about what this is supposed to do:
Draw vapor from the tank, so it's not in the cab. The charcoal neutralizes the vapor and what can't be neutralized is burnt in your motor. The vacuum port also provides the "draw" from the tank into the canister.


Now the really fun fact: Activated Carbon (charcoal) is really only good for about three days. Which is why some canisters have three ports, in case the charcoal gets clogged or overflows fuel instead of vapor.

[myoldchevytruck]

Nice. You have done well my friend. Thanks for all your help. I gave you some rep points.

[BLACK AND BLUE 67-72]

You need the two lines in order for it to vent out of your tank, if you pulled out the sender you would see that the vent line is short, so it will not suck fuel out of your tank.

[FormerMember]

Originally Posted by myoldchevytruck

Nice. You have done well my friend. Thanks for all your help. I gave you some rep points.

You're welcome, I am glad I could help.

Originally Posted by BLACK AND BLUE 67-72

You need the two lines in order for it to vent out of your tank, if you pulled out the sender you would see that the vent line is short, so it will not suck fuel out of your tank.

Yep, very good point, make sure the short output in the sending unit is hooked to the charcoal caninster or you'll be sucking gas.

[myoldchevytruck]

Thanks guys. I'm gonna order a 2 line sending unit from brothers right now. Quick thought about that vent nipple on the passenger side of the tank (excuse me if I already addressed it) Will it also go to the canister? If so, since theres only 2 ports, will I still need to vent to carb/intake?

[sneakysnake]

Just to throw this in, the older tanks had vented fuel caps as the newer ones with the emissions canasters didnt so to work properly you might check your cap too.

[myoldchevytruck]

Originally Posted by sneakysnake

Just to throw this in, the older tanks had vented fuel caps as the newer ones with the emissions canasters didnt so to work properly you might check your cap too.

This is true. The 67'-71' tanks have a 2 inch fuel neck allowing a vented gas cap. The 72' tanks on the other hand had a smaller fuel neck, 1-1/4" if I'm correct. These caps, as you stated, are not vented. Thanks for the FYI.

[BLACK AND BLUE 67-72]

Yes you will still have to hook it to the carb in order for the vacuum to suck the vapors out of the tank.

[myoldchevytruck]

looks like I'll be looking for a canister cap with three ports. again, thanks.

[FormerMember]

Originally Posted by myoldchevytruck

Thanks guys. I'm gonna order a 2 line sending unit from brothers right now. Quick thought about that vent nipple on the passenger side of the tank (excuse me if I already addressed it) Will it also go to the canister? If so, since theres only 2 ports, will I still need to vent to carb/intake?

I would block that nipple off and run the fittings from the two port sending unit.

You could of course, if you had a single fitting sending unit already, run a line from that nipple to the charcoal canister.

[myoldchevytruck]

Originally Posted by grendel

I would block that nipple off and run the fittings from the two port sending unit.

You could of course, if you had a single fitting sending unit already, run a line from that nipple to the charcoal canister.

Grendel, If running the single fitting sending unit will work, I think Ima gonna do that. It is of coarse the correct one with a 3/8" inch fitting for as 350 v-8with automatic.

[FormerMember]

Originally Posted by myoldchevytruck

Grendel, If running the single fitting sending unit will work, I think Ima gonna do that. It is of coarse the correct one with a 3/8" inch fitting for as 350 v-8with automatic.

Well, sounds like you saved some money and get the fumes out of your cab with the addition of a dual port vacuum canister.

You probably have that, too...

[Stock72c10]

I put all new hoses on my EEC this weekend. Mine had the one line coming from the sending unit with a small piece of rubber hose attaching to a metal line that follows the passenger side frame up to right below the bottom radiator hose. From there there was about a 3' section of rubber hose that attached to the carbon canister (right behind the passenger side headlight). There was an overflow hose that comes off the neck of the carbon canister (right below the cap) and then there is the line that goes to the carb which is connected to the top of the carbon canister cap. Hope that helps.