Closed Vent to Open Vent Fuel System - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jedab72C10 · 10-08-2004, 05:55 PM

Greetings all, great board, been reading for about a week and would like to ask some advice. We inherited Dads 72 Chevy pickup C10, 350, AT. He was about 95% complete on a total restoration when he passed away. We'd like to finish it but I am undecided on one particular thing.
This model has the tank behind the seat. Its a small tank so Dad added a saddle tank on each side. Now there is a 15 gal on each side along with the 8 gal behind the seat. There is a switch that you turn to determine which tank to choose. There is one problem with this that was not thought out or finished. This model uses a closed fuel system. If you use the middle tank its fine. The problem is when you use one of the saddle tanks. The return builds so much pressure into the tank behind the seat, it could literally explode if you don't switch back to it or use it to relieve that pressure from the return. It would be difficult for me to put a return to whichever side tank I was using to keep the system a closed system. So I think I should open it, use a vented cap, and cap the returns to the tank behind the seat. What can I do about the fuel pump ? New one ? or cap the return for that ? If you have any other suggestions for this they would be appreciated. It would be really nice to eliminate that gas smell in the cab too, I am replacing some hoses and the fuel sending unit which didn't work, to get the gas guage back too. I don't have senders for the saddle tanks. Does anyone have a slick way to determine fuel levels in the saddle tanks ? Thanks in advance for all of your input.

*rage'nrat638* · 10-08-2004, 08:11 PM

welcome to the board.....

well.....they make a 3 way valve that turns on each tank.....
and yes there should be vented caps on the gas tanks no mater what.....
just the sloushing of the gas will build pressure in the tanks....
i also have a 3 way switch that shows the fuel level in each tank....but i have senders in each one.......
use a stick to check level,,,,or watch the mile'S ran on each tank ....or run it dry....and switch......
the RAGENRAT638

jedab72C10 · 10-08-2004, 11:10 PM

What does everyone recommend with the fuel pump ? Can the return be pinched or plugged ? or do you recommend purchasing a fuel pump with with just an the single input line ? Thanks for your response

chickenwing · 10-08-2004, 11:38 PM

Welcome from Northern California! Sorry to hear about your Daddy. Hope the truck lets you re-live all the good times..
I have a VDO sending unit in my aux tank. Use whatever brand you want. Think it uses 0-90 ohm sweep. Went electric fuel pump on mine, no more oil leaks at the fuel pump. Vented cap on both tanks. Capped of my return lines.

68LSS1 · 10-09-2004, 04:24 AM

You could always run a charcoal canister. The three tanks in and one out (to a vacuum source). That would keep your fuel system closed. They also make check valves that allow pressure through but not gas. It would mean running a vent line off each tank though. And welcome!

MOTHERTRUCKERS · 10-09-2004, 07:05 AM

Brian e-mail your e-mail address the pm is not working for some reason.

badpeanut · 12-29-2004, 05:33 PM

I have a similar problem. Did you end up going vented or closed system?

10-08-2004, 05:55 PM	#1
jedab72C10 Registered User Join Date: Oct 2004 Posts: 3	Closed Vent to Open Vent Fuel System Greetings all, great board, been reading for about a week and would like to ask some advice. We inherited Dads 72 Chevy pickup C10, 350, AT. He was about 95% complete on a total restoration when he passed away. We'd like to finish it but I am undecided on one particular thing. This model has the tank behind the seat. Its a small tank so Dad added a saddle tank on each side. Now there is a 15 gal on each side along with the 8 gal behind the seat. There is a switch that you turn to determine which tank to choose. There is one problem with this that was not thought out or finished. This model uses a closed fuel system. If you use the middle tank its fine. The problem is when you use one of the saddle tanks. The return builds so much pressure into the tank behind the seat, it could literally explode if you don't switch back to it or use it to relieve that pressure from the return. It would be difficult for me to put a return to whichever side tank I was using to keep the system a closed system. So I think I should open it, use a vented cap, and cap the returns to the tank behind the seat. What can I do about the fuel pump ? New one ? or cap the return for that ? If you have any other suggestions for this they would be appreciated. It would be really nice to eliminate that gas smell in the cab too, I am replacing some hoses and the fuel sending unit which didn't work, to get the gas guage back too. I don't have senders for the saddle tanks. Does anyone have a slick way to determine fuel levels in the saddle tanks ? Thanks in advance for all of your input.

10-08-2004, 11:38 PM	#4
chickenwing Lovin' Life in Miss.! Join Date: Mar 2004 Location: Puckett, Mississippi Posts: 1,937	Welcome from Northern California! Sorry to hear about your Daddy. Hope the truck lets you re-live all the good times.. I have a VDO sending unit in my aux tank. Use whatever brand you want. Think it uses 0-90 ohm sweep. Went electric fuel pump on mine, no more oil leaks at the fuel pump. Vented cap on both tanks. Capped of my return lines. __________________ The truck... you hear that? No really, you did hear that?!!!

10-09-2004, 04:24 AM	#5
68LSS1 Registered User Join Date: Dec 2002 Location: Tampa Posts: 1,191	You could always run a charcoal canister. The three tanks in and one out (to a vacuum source). That would keep your fuel system closed. They also make check valves that allow pressure through but not gas. It would mean running a vent line off each tank though. And welcome! __________________ '68 Short Step LS1/T56, Hydratech, Fatman Fabrications Stage III, Baer, Hot Rods to Hell, US Body, S&W, etc

10-09-2004, 07:05 AM	#6
MOTHERTRUCKERS Registered User Join Date: Dec 1999 Location: BRADENTON FLA Posts: 3,269	Brian e-mail your e-mail address the pm is not working for some reason. __________________ Rest in Peace Ed. Thanks for all the good times.

10-08-2004, 08:11 PM	#2
rage'nrat638 Account Suspended Join Date: Mar 2003 Location: THE FALL GUY CHICAGO IL Posts: 5,883	welcome to the board..... well.....they make a 3 way valve that turns on each tank..... and yes there should be vented caps on the gas tanks no mater what..... just the sloushing of the gas will build pressure in the tanks.... i also have a 3 way switch that shows the fuel level in each tank....but i have senders in each one....... use a stick to check level,,,,or watch the mile'S ran on each tank ....or run it dry....and switch...... the RAGENRAT638

10-08-2004, 11:10 PM	#3
jedab72C10 Registered User Join Date: Oct 2004 Posts: 3	What does everyone recommend with the fuel pump ? Can the return be pinched or plugged ? or do you recommend purchasing a fuel pump with with just an the single input line ? Thanks for your response

12-29-2004, 05:33 PM	#7
badpeanut Not a bad nut after all.. Join Date: Dec 2000 Location: ND Posts: 1,756	I have a similar problem. Did you end up going vented or closed system?



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.