Venting that tank?
Thread Starter
Instructor
Joined: Apr 2005
Posts: 140
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Venting that tank?
Hi, I removed the gas tank while I was already in there to replace the differential. I found the tank vapor vent on the driver side to be plugged. I don't think that the gas cap is vented but I'm not sure how to tell either. There is both fuel feed and fuel return connected from the tank to the fuel pump. The vapor canister in the engine bay is missing, as is the fuel separator that should be mounted to the driver's side of the tank. I figure I need some venting to equalize pressure to the atmosphere or there will be problems with over- / underpressure in the tank.
I'm thinking about some possible options here.
1 plugging the vapor connection to the tank again OR
2 leaving the vapor connection open with some short pipe pointing upwards like a snorkel and a filter to prevent dirt from entering the tank OR
3 connecting the vapor from the tank to the vapor line without any additional hardware like separator or canister OR
4 getting the separator and canister and connecting everything by the book.
I really want to avoid buying the missing hardware. Is any of the other options a good solution?
Please chime in with your opinions here guys. I don't mind hints of gas smell as long as the garage wont blow up
I'm thinking about some possible options here.
1 plugging the vapor connection to the tank again OR
2 leaving the vapor connection open with some short pipe pointing upwards like a snorkel and a filter to prevent dirt from entering the tank OR
3 connecting the vapor from the tank to the vapor line without any additional hardware like separator or canister OR
4 getting the separator and canister and connecting everything by the book.
I really want to avoid buying the missing hardware. Is any of the other options a good solution?
Please chime in with your opinions here guys. I don't mind hints of gas smell as long as the garage wont blow up
Melting Slicks
Joined: Jan 2007
Posts: 2,589
Likes: 5
From: Salisbury Maryland
I see you have a 72.
I just recently replaced my 69 tank due to a pinhole leak. Bubba had gotten to it before me and I had a similar situation. The return line was capped off and the tank was not correct; i.e. there was no vent fitting(later 69 I believe) on the tank at all. I didn't have a pressure problem though because the cap was vented.
If you don't want to buy all the replacement stuff just make sure you do get a vented gas cap. Don't "snorkel" the return or there will always be the smell of gas present.
Good Luck!
P.S. Don't forget to disconnect the battery.
I just recently replaced my 69 tank due to a pinhole leak. Bubba had gotten to it before me and I had a similar situation. The return line was capped off and the tank was not correct; i.e. there was no vent fitting(later 69 I believe) on the tank at all. I didn't have a pressure problem though because the cap was vented.
If you don't want to buy all the replacement stuff just make sure you do get a vented gas cap. Don't "snorkel" the return or there will always be the smell of gas present.
Good Luck!
P.S. Don't forget to disconnect the battery.
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
Go to your Chevy parts counter,..ask for fuel cap number: 3952701. It's a vented cap for 68-69 Vettes. Vented caps rattle when you shake them,..much like your PCV valve. 'Vented' means air will be allowed in to the tank to replace spent fuel, but won't allow fumes or fuel out. Also, make sure the nipple for the EVAP system is indeed blocked off.
Good luck!
Good luck!
Thread Starter
Instructor
Joined: Apr 2005
Posts: 140
Likes: 0
Ok, thanks guys.
So if I understand it right, a vented cap is a one-way valve to equalize pressure for the spent fuel, thus removing the underpressure problem.
Overpressure in the tank and fuel delivery before the pump is not a problem?
Bringing out the old trusty pressure equation pv=nRT and assuming that worst case scenario is an increase in temperature by 30 degrees kelvin / centigrade means that pressure will rise to 10% overpressure. Would anything in the fuel system be affected negatively by this?
So if I understand it right, a vented cap is a one-way valve to equalize pressure for the spent fuel, thus removing the underpressure problem.
Overpressure in the tank and fuel delivery before the pump is not a problem?
Bringing out the old trusty pressure equation pv=nRT and assuming that worst case scenario is an increase in temperature by 30 degrees kelvin / centigrade means that pressure will rise to 10% overpressure. Would anything in the fuel system be affected negatively by this?
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
You're correct,..she'll pressurize a bit from the agitation of the fuel, heat from the exhaust, and atmospheric pressure changes.
When you open the fuel cap, she'll sometimes belch at you. It's this belching that the EPA was trying get rid of, so enter the EVAP system in 1970. Even today, at the gas station, you see 'umbrellas' on the pump nozzles that attempt to prevent fumes from escaping.
FWIW.
When you open the fuel cap, she'll sometimes belch at you. It's this belching that the EPA was trying get rid of, so enter the EVAP system in 1970. Even today, at the gas station, you see 'umbrellas' on the pump nozzles that attempt to prevent fumes from escaping.
FWIW.
