Fuel Tank Questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Jayschevy · 03-03-2013, 07:20 PM

I have a few questions about the stock gas tank that's in the cab of my 71. I think I know but I need to know for sure which lines from the tank are the supply line and which one is the return line.
I'm guessing that the line coming out the top of the tank is the supply line, correct?
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Also am I correct to say that the line coming from the outside running alone the bottom of the tank is the return line? If so, this line runs up the passinger side of the back window and another line runs to the tank. Where does it go?
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I just need to make sure that I know for sure which lines are the supply and return lines because I'm planning on taking the tank out of the cab and putting a Boyd tank in the rear.

71meangreenc10 · 03-03-2013, 07:21 PM

Its a vent line from the charcoal cannister.

Smitty

Jayschevy · 03-03-2013, 07:31 PM

So is the vent line a return line? And is the supply line coming from the top of the tank (sending unit)?

68gmsee · 03-03-2013, 07:45 PM

You are correct. The line coming out of the top of the tank is supply line to the fuel pump.

I'm not familiar with the other lines but as mentioned more than likely just vent lines for the tank. However, you say one line runs up the passenger side of the back window. Where does it connect to the tank from there? The vent lines I'm familiar with are doubled up with the sending unit supply line.

If I had to guess, someone replaced the sending unit and used a non vented unit instead of the vented one.

1969K10 · 03-03-2013, 07:40 PM

no return line. the fumes from the charcoal canister are vented back to the fuel tank.

Jayschevy · 03-03-2013, 08:21 PM

The gas line running up the side of the tank comes from under the truck. It doesn't come from the tank so I'm sure it's not a vent line. I'm using a self venting gas cap.

Jayschevy · 03-04-2013, 11:04 AM

Anyone?

LT102 · 03-04-2013, 11:22 AM

I just pulled the tank on my 71' C20 and there was only one line, the one running to the top of the tank where the sending unit wire attaches. I will get the Assembly Manual out and see if these lines are shown. Got my curiosity going.

Jayschevy · 03-04-2013, 01:42 PM

Quote:

Originally Posted by LT102

I just pulled the tank on my 71' C20 and there was only one line, the one running to the top of the tank where the sending unit wire attaches. I will get the Assembly Manual out and see if these lines are shown. Got my curiosity going.

The second line came from under the truck trough the floor. It runs along the bottom of the tank than up the side of the window on the passinger side. Than it runs into the top side of the tank. I'm guessing it's a return line.

cdowns · 03-04-2013, 01:50 PM

it looks to me as you do not have the original 71 c10 gas tank
the original 71 c10 had the one supply line from the sender and then another line from the top passenger side of the tank that ran up the door frame into a high loop to prevent siphoning then down thru floor up to charcoal cannister to carb // and that roundabout system was your tank vent/// the 71c10 gastank didnot have a vented gascap

c20 did not have that vent

Leftlane · 03-04-2013, 04:08 PM

My original '71 tank is the same as yours.
1 fuel feed line, 1 vent loop up the B-pillar to the canister.
No return.
350 th350 factory A/C.
Posted via Mobile Device

ChevyCruizer · 03-04-2013, 01:48 PM

The lines that do up into the cab will come out easily if you want to look at them. They just go up about a foot and then do a 180 and hook back up to them self. Understand?

Not all trucks have a return line. Look at your fuel pump, if it has 2 ports then no return line. If it has 3 (usually 1 is smaller) then it has a return line.

In the picture in post 1, that pickup is not for a return line system. If it was it would have a 2nd port and that would be where the return would go. I can get a pict of a very rusty pickup that has the second port once I get home.

Thanks, John

ChevyCruizer · 03-04-2013, 09:11 PM

As promised here are the pictures. First one shown the outside of the tank sender unit with the 2nd return line. The second shows the inside so you can see what it does.

Told you it was crusty. LOL

I agree with the other comment, just run a feed line and dont worry about the other hoses. Just make sure your fuel pump (if using an engine mounted) only has the two ports like I mentioned above.

03-03-2013, 07:20 PM	#1
Jayschevy Registered User Join Date: May 2012 Location: Eastern, NC Posts: 429	Fuel Tank Questions I have a few questions about the stock gas tank that's in the cab of my 71. I think I know but I need to know for sure which lines from the tank are the supply line and which one is the return line. I'm guessing that the line coming out the top of the tank is the supply line, correct? [IMG][/IMG] Also am I correct to say that the line coming from the outside running alone the bottom of the tank is the return line? If so, this line runs up the passinger side of the back window and another line runs to the tank. Where does it go? [IMG][/IMG] I just need to make sure that I know for sure which lines are the supply and return lines because I'm planning on taking the tank out of the cab and putting a Boyd tank in the rear.

03-03-2013, 07:21 PM	#2
71meangreenc10 Its a Truck Thing...... Join Date: Dec 2004 Location: Sierra Vista, Arizona Posts: 3,179	Re: Fuel Tank Questions Its a vent line from the charcoal cannister. Smitty __________________ 71 C10 283/3SPD Full Resto 71 GMC 1500 Sierra Grande http://67-72chevytrucks.com/vboard/s...d.php?t=518599 70 C10 Suburban Former military GSA truck. 72 Chevy Blazer 4X4, Sloppy Jo, Mountain Climber. Wife says no more trucks. http://67-72chevytrucks.com/vboard/s...d.php?t=707378 72 GMC 1 Ton Motor Home, wife said no more trucks until she saw this one. Gen 3 6.0/4L80E 4.10 http://67-72chevytrucks.com/vboard/s...d.php?t=761110 68 GMC Suburban was 3/4 ton, now 1/2.Wife shook her head 71 C30 Wrecker 71 C20 Scott-Bilt As weird as it gets..BB Cheyenne AC Truck 68 GMC Long Stepside. They keep following me home 69 C30 Former Motor Home, Flat Bed time 70 G20 Red-E-Kamp Conversion "I'm your Boogy Van"

03-03-2013, 07:31 PM	#3
Jayschevy Registered User Join Date: May 2012 Location: Eastern, NC Posts: 429	Re: Fuel Tank Questions So is the vent line a return line? And is the supply line coming from the top of the tank (sending unit)?

03-03-2013, 07:45 PM	#4
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Fuel Tank Questions You are correct. The line coming out of the top of the tank is supply line to the fuel pump. I'm not familiar with the other lines but as mentioned more than likely just vent lines for the tank. However, you say one line runs up the passenger side of the back window. Where does it connect to the tank from there? The vent lines I'm familiar with are doubled up with the sending unit supply line. If I had to guess, someone replaced the sending unit and used a non vented unit instead of the vented one. __________________ 68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive...

03-03-2013, 07:40 PM	#5
1969K10 Senior Member Join Date: Jul 2004 Location: Clarks Hill, Indiana Posts: 733	Re: Fuel Tank Questions no return line. the fumes from the charcoal canister are vented back to the fuel tank. __________________ 1969 K10 - V8, 465, 205, 12 bolt, D44 2002-current 1969 K20 - V8, 465, 221, Eaton, D44 2012-current Nothin' but drums on all 4 corners! past horses in the stable 72 C10-short step (97-02), 68 C10-long fleet (06-12)

03-03-2013, 08:21 PM	#6
Jayschevy Registered User Join Date: May 2012 Location: Eastern, NC Posts: 429	Re: Fuel Tank Questions The gas line running up the side of the tank comes from under the truck. It doesn't come from the tank so I'm sure it's not a vent line. I'm using a self venting gas cap.

03-04-2013, 11:04 AM	#7
Jayschevy Registered User Join Date: May 2012 Location: Eastern, NC Posts: 429	Re: Fuel Tank Questions Anyone?

03-04-2013, 11:22 AM	#8
LT102 Registered User Join Date: Oct 2012 Location: Greenville, Oh Posts: 72	Re: Fuel Tank Questions I just pulled the tank on my 71' C20 and there was only one line, the one running to the top of the tank where the sending unit wire attaches. I will get the Assembly Manual out and see if these lines are shown. Got my curiosity going.

03-04-2013, 01:50 PM	#10
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Fuel Tank Questions it looks to me as you do not have the original 71 c10 gas tank the original 71 c10 had the one supply line from the sender and then another line from the top passenger side of the tank that ran up the door frame into a high loop to prevent siphoning then down thru floor up to charcoal cannister to carb // and that roundabout system was your tank vent/// the 71c10 gastank didnot have a vented gascap c20 did not have that vent __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

03-04-2013, 04:08 PM	#11
Leftlane Registered User Join Date: Dec 2002 Location: St. Louis, MO Posts: 118	Re: Fuel Tank Questions My original '71 tank is the same as yours. 1 fuel feed line, 1 vent loop up the B-pillar to the canister. No return. 350 th350 factory A/C. Posted via Mobile Device __________________ 1971 C10 SWB 350/350 A/C PS PDB

03-04-2013, 01:48 PM	#12
ChevyCruizer 17's too small Join Date: Oct 2004 Location: Las Vegas, NV Posts: 335	Re: Fuel Tank Questions The lines that do up into the cab will come out easily if you want to look at them. They just go up about a foot and then do a 180 and hook back up to them self. Understand? Not all trucks have a return line. Look at your fuel pump, if it has 2 ports then no return line. If it has 3 (usually 1 is smaller) then it has a return line. In the picture in post 1, that pickup is not for a return line system. If it was it would have a 2nd port and that would be where the return would go. I can get a pict of a very rusty pickup that has the second port once I get home. Thanks, John __________________ 68 C10 SWB SS 5 lug power disc brake conversion 2.5 inch drop spindles van tilt column Air Ride Technologies Cool Ride air bag kits Performance Online tubular upper control arms and shock relocator kits ECE super track panhard bar 1 piece side windows

03-04-2013, 09:11 PM	#13
ChevyCruizer 17's too small Join Date: Oct 2004 Location: Las Vegas, NV Posts: 335	Re: Fuel Tank Questions As promised here are the pictures. First one shown the outside of the tank sender unit with the 2nd return line. The second shows the inside so you can see what it does. Told you it was crusty. LOL I agree with the other comment, just run a feed line and dont worry about the other hoses. Just make sure your fuel pump (if using an engine mounted) only has the two ports like I mentioned above. Attached Images __________________ 68 C10 SWB SS 5 lug power disc brake conversion 2.5 inch drop spindles van tilt column Air Ride Technologies Cool Ride air bag kits Performance Online tubular upper control arms and shock relocator kits ECE super track panhard bar 1 piece side windows



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