Why would a vented gas tank
Thread Starter
Melting Slicks
Joined: Jul 2001
Posts: 2,609
Likes: 12
From: Massapequa Park NY
Why would a vented gas tank
not vent?? Made some more progress reassembling the car and started up the engine for the first time. 70 LS-5 I have a new vented tank, non venting gas cap & am using an original fuel pump. After running the engine for 45 min or so I removed the gas which allowed a large in rush of air.
Anyone else ever experience this? Figured I'd check to see if something is wrong or blocking the vent before I contact the supplier.
Thanks
Jim
Anyone else ever experience this? Figured I'd check to see if something is wrong or blocking the vent before I contact the supplier.
Thanks
Jim
Thread Starter
Melting Slicks
Joined: Jul 2001
Posts: 2,609
Likes: 12
From: Massapequa Park NY
There is no charcoal canister, supply & return lines on the right side frame rail. Fuel pump has supply & return lines as well as the carb feed. Everything is new, no clogged lines, but I still need to see if I can look at the vent on the top of the tank with a mirror.
I know I can just install a vented cap, but this setup should work...
Thanks
Jim
Thread Starter
Melting Slicks
Joined: Jul 2001
Posts: 2,609
Likes: 12
From: Massapequa Park NY
Thanks
Jim
Burning Brakes
Joined: Mar 2005
Posts: 1,139
Likes: 0
From: Salina Kansas
Soon after I bought my '76, I drove it home from about 120 miles away in about 100 degree weather. I pull up to the house and hear this whistling sound. It is coming from the gas cap. I open the cap and a bunch of hot gas vapor shoots out and the gas was actually boiling.
Guess what happened? Top of one of my mufflers rusted out and was shooting hot air up onto the bottom of the gas tank for 2 hours. Glad I'm not a smoker. You might check your mufflers.
Guess what happened? Top of one of my mufflers rusted out and was shooting hot air up onto the bottom of the gas tank for 2 hours. Glad I'm not a smoker. You might check your mufflers.
Melting Slicks
Joined: Dec 2005
Posts: 2,441
Likes: 0
If you're car came with a charcoal canister you should have a vent line running the length of the drivers side to the canister. The tank end of this line should connect to a tank mounted vapor separator via a hose, and another short rubber hose connects the separator to the tank. There should be a nipple available on the drivers side of the tank that accepts the hose from the separator.
Last edited by shafrs3; Aug 29, 2007 at 12:47 PM.
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Thread Starter
Melting Slicks
Joined: Jul 2001
Posts: 2,609
Likes: 12
From: Massapequa Park NY
If you're car came with a charcoal canister you should have a vent line running the length of the drivers side to the canister. The tank end of this line should connect to a tank mounted vapor separator via a hose, and another short rubber hose connects the separator to the tank. There should be a nipple available on the drivers side of the tank that accepts the hose from the separator.
This version, 70 LS5 didn't come with a charcoal canister. Two lines on the right hand side for supply and return/vent from the tank to the fuel pump. Gas tank has a vent also in the top. Yet it doesn't seem to be allowing air in to replace the consumed gas. Every catalog ( well almost every
) listing I looked at shows a non vented cap for 70 - 74.If the tank is vented, why would I need a vented cap?
Top of one of my mufflers rusted out and was shooting hot air up onto the bottom of the gas tank for 2 hours. Glad I'm not a smoker. You might check your mufflers.
Thanks
Jim
Melting Slicks
Joined: Dec 2005
Posts: 2,441
Likes: 0
The only explanation is the vent is plugged. I can give you an easy fix, drill a small hole in the bottom of that gas cap. Since I've removed my canister and plugged the tank vent I needed a vented cap, I did this to avoid buying another cap.
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
If you have the fuel tank original to your 70, it's designed with the evap system. There should be a fuel separator on the driver' side of the tank. My guess is, somebody removed the FS and plugged the nipple on the tank. And if you're using your original non-vented cap, vacuum is building in the tank.
So, either purchase a vented cap or replace the evap system (includes fuel separator, charcoal can, steel lines, hoses, etc.). A vented cap will allow air "in" to replace spent fuel but won't allow fumes or fuel "out" for obvious reasons. A good vented cap will "rattle" which means the little check valve is good.
1969 and earlier cars which had a vented cap will sometimes "whoosh" when the cap is removed. As fuel in the tank is agitated (driving) and heated (exhaust) a bit of pressure can build and fumes can blow out when you open the cap. Perfectly normal for 69 and earlier cars. But not environmentally friendly so the "closed" system or evap system starting in 70 was utilized.
So, either purchase a vented cap or replace the evap system (includes fuel separator, charcoal can, steel lines, hoses, etc.). A vented cap will allow air "in" to replace spent fuel but won't allow fumes or fuel "out" for obvious reasons. A good vented cap will "rattle" which means the little check valve is good.
1969 and earlier cars which had a vented cap will sometimes "whoosh" when the cap is removed. As fuel in the tank is agitated (driving) and heated (exhaust) a bit of pressure can build and fumes can blow out when you open the cap. Perfectly normal for 69 and earlier cars. But not environmentally friendly so the "closed" system or evap system starting in 70 was utilized.
Last edited by 73, Dark Blue 454; Aug 29, 2007 at 11:04 PM.
Thread Starter
Melting Slicks
Joined: Jul 2001
Posts: 2,609
Likes: 12
From: Massapequa Park NY
If you have the fuel tank original to your 70, it's designed with the evap system. There should be a fuel separator on the driver' side of the tank. My guess is, somebody removed the FS and plugged the nipple on the tank. And if you're using your original non-vented cap, vacuum is building in the tank.
So, either purchase a vented cap or replace the evap system (includes fuel separator, charcoal can, steel lines, hoses, etc.). A vented cap will allow air "in" to replace spent fuel but won't allow fumes or fuel "out" for obvious reasons. A good vented cap will "rattle" which means the little check valve is good.
1969 and earlier cars which had a vented cap will sometimes "whoosh" when the cap is removed. As fuel in the tank is agitated (driving) and heated (exhaust) a bit of pressure can build and fumes can blow out when you open the cap. Perfectly normal for 69 and earlier cars. But not environmentally friendly so the "closed" system or evap system starting in 70 was utilized.
So, either purchase a vented cap or replace the evap system (includes fuel separator, charcoal can, steel lines, hoses, etc.). A vented cap will allow air "in" to replace spent fuel but won't allow fumes or fuel "out" for obvious reasons. A good vented cap will "rattle" which means the little check valve is good.
1969 and earlier cars which had a vented cap will sometimes "whoosh" when the cap is removed. As fuel in the tank is agitated (driving) and heated (exhaust) a bit of pressure can build and fumes can blow out when you open the cap. Perfectly normal for 69 and earlier cars. But not environmentally friendly so the "closed" system or evap system starting in 70 was utilized.
So, I guess I'll drop the tank to make sure nothing is blocking the vent. The supplier has already offered to swap the gas cap with a vented version even though it shouldn't be needed.
Jim
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Thanks for all the replies guys. Did some more research re: the charcoal canister, EEC system. In 1970 all cars with Ca. emissions,NA9, got the charcoal canister. In 1971 it was installed in all Corvettes. My car was sold new in SC, and did not come with EEC. I took the body off back in 2002, no lines for EEC system were present.
So, I guess I'll drop the tank to make sure nothing is blocking the VENT. The supplier has already offered to swap the gas cap with a vented version even though it shouldn't be needed.
Jim
So, I guess I'll drop the tank to make sure nothing is blocking the VENT. The supplier has already offered to swap the gas cap with a vented version even though it shouldn't be needed.
Jim
On the earlier tanks "the tank" is not vented but the "cap" is.
