bb1970

Fuel leaking from vent tube

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Hey guys. I have fuel that leaks from the vent tube. I would expect a little leaking when full under hard acceleration or on a hill. But this is all the time. worse if full tank. I just filled up. Drove around some. Got out of the car to a stout fuel smell. Inspected under the hood, down the fuel line along the frame. I get to the rear of the car and it leaked so bad gas was dripping from the rear bumper. It's like pressure is building in the tank and forcing fuel out of the vent tube. Should I try a vented cap?? Or disconnect return line?

Edited by bb1970 (see edit history)

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Try a new correct (the one speced for your car) gas cap first. Many times the round rubber(?) seal in your gas cap goes to heck, and creates a situation like you are describing. John

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I have leakage from my vent tube also. Is anyone else experiencing this crap? Multiple times, while cruising, I’ve had guys run up to me at a light to tell me I’m leaking. I’ve put it in parked, ran back to check & I can see it pouring out of the vent tube. It’s NOT coming from gas cap. My non vented gas cap is new. 
 

Does anyone have a fix for this other than not topping off my tank? What’s the use in having a 20 gallon tank if we can only fill up to 17??

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11 hours ago, RockinRiviDad said:

I have leakage from my vent tube also. Is anyone else experiencing this crap? Multiple times, while cruising, I’ve had guys run up to me at a light to tell me I’m leaking. I’ve put it in parked, ran back to check & I can see it pouring out of the vent tube. It’s NOT coming from gas cap. My non vented gas cap is new. 
 

Does anyone have a fix for this other than not topping off my tank? What’s the use in having a 20 gallon tank if we can only fill up to 17??

These cars do this because of the angle of the filler neck making the end of the neck very low in relation to the top of the tank. My car does this and my Dad's

65 always did that from when it was brand new if you filled it up all the way till it clicks off. I always fill mine when it gets to the same place on the gas gauge

then I always but in 13 gallons and this gets me to a little over 3/4 on the gauge and it never leaks when I do that. The problem is that

the license plate is so low in the bumper on these cars that the neck is very low and almost straight instead of curling upward.....it had

to be this way in order to hide the filler behind the license plate. My 69 GTO has the same kind of setup with the low neck but Pontiac solved the problem by running the vent hose to a metal tube that goes way up into the trunk behind the trunk lid striker then comes back down through the trunk floor. The early Riviera vent hose stays under the trunk floor thus the leaking problem.

Edited by Seafoam65 (see edit history)
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Make sure the vent tube rubber does not have a split in it or another leak, especially where the clamp holds it on to the tank vent. Modern fuels eat up old rubber hoses.

 

Make sure the rubber vent tube goes up high in a loop after it exits the tank before pointing toward the ground. I think there's a picture of this in the shop manual.

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All 2nd gen. Riviera eliminated this potential problem by placing a metal expansion loop above the gas tank.

It is found in the trunk by the rear right wheel well.

Fuel will expand with warmer temperatures, so allow for this when filling the tank.                                            

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Thx for the replies, gentlemen. Kind of a lame design if u ask me
 

My hose is new, NOT cracked. I did try to pull it up higher to create a bigger loop. But there isn’t much room behind the rear bumper for much more than what I have. I may try drilling 2 holes in the trunk floor behind the trunk lid striker & loop hose up thru trunk like u the 2nd gen design u guys mentioned. 
 

thx again guys

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Has anyone tried putting a check valve in the vent line to prevent the gas surge from happening? 

 

Kevin

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1 minute ago, kegart said:

check valve in the vent line 


I’ve been talking about that. Everyone tells me that it won’t work. It WILL let air in to displace fuel consumption. But won’t let vapors out when expansion happens on hot days. 
 

True or false? 🤷🏻‍♂️🤷🏻‍♂️

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I don't know for sure, but is the vent also used to allow expanding air to escape during hot weather?  If not, a valve should work (IMHO.)

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10 minutes ago, RivNut said:

is the vent also used to allow expanding air to escape during hot weather?


I don’t know either. But it’s an open port & inadvertently will allow expanding air out.
 

A lesson learned the hard way was when I first got my car on the road I had that port capped. I can’t remember how I caught it but while out cruising on a hot day my fuel tank looked like a balloon 😳. My buddy thought it was gonna blow haha. I simply open the fuel cap & the expanding air escaped haha. Then I drove straight to Pep Boys for a hose haha

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1 minute ago, arnulfo de l.a. said:

Top mine off all the time. Have not had that problem yet.....


Do u have a big loop in the hose that goes over your filler neck?

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3 hours ago, 1965rivgs said:

Just an FYI...pretty sure the original fuel cap is vented

Tom Mooney


So Buick used a vented fuel cap on a vented fuel tank?

 

I will post a pic of my cap. There is no hole on the outside of it to indicate that it is a vented cap. But the inside of the cap has what looks like a little filter?? 🤷🏻‍♂️

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7 hours ago, RockinRiviDad said:


So Buick used a vented fuel cap on a vented fuel tank?

 

I will post a pic of my cap. There is no hole on the outside of it to indicate that it is a vented cap. But the inside of the cap has what looks like a little filter?? 🤷🏻‍♂️

 

I agree with Tom. I have an NOS gas cap on my 63 and am pretty sure it is vented as was the one it replaced. I have the large loop around the filler neck as well. I fill my car to the brim and have never had a leaking problem. The only time I ever had a problem is when I parked with a full tank on a backwards incline. This is when the low filler neck came into play as Winston mentioned. In that situation I had gas leak out around the gas cap.

 

Bill

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9 hours ago, RockinRiviDad said:


So Buick used a vented fuel cap on a vented fuel tank?

 

I will post a pic of my cap. There is no hole on the outside of it to indicate that it is a vented cap. But the inside of the cap has what looks like a little filter?? 🤷🏻‍♂️

I`m not suggesting that I do or do not agree with the original engineering...just stating what I believe to be a fact in that fuel tank venting is being discussed in this thread.

Tom M

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16 hours ago, RockinRiviDad said:
16 hours ago, RockinRiviDad said:


So Buick used a vented fuel cap on a vented fuel tank?

 

I will post a pic of my cap. There is no hole on the outside of it to indicate that it is a vented cap. But the inside of the cap has what looks like a little filter?? 🤷🏻‍♂️

 

 

First picture is of my gas cap. Vented as you can see.

 

Picture number 2 shows my venting hose configuration. Right or wrong I don't know.

 

The 3rd and 4th pictures show the gas cap that was on my car when I purchased it . Also a vented cap. You are welcome to have it for postage if you would like it.

 

Bill

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Bill, thank u for the pix. Can u explain what is attached to the end of your vent hose? Is that a one way check valve?
 

Also, how does a vented cap vent if there is no hole on the outside/top of the cap??


I am confused what these vented caps are suppose to look like. My cap doesn’t say “vented” like the one Bill posted. But mine does have the yellowish looking filter like element on inside/bottom of the cap. Like Bill’s new cap, my cap also does NOT have a hole in the outside/top of the cap

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5 hours ago, RockinRiviDad said:

Bill, thank u for the pix. Can u explain what is attached to the end of your vent hose? Is that a one way check valve?
 

Also, how does a vented cap vent if there is no hole on the outside/top of the cap??


I am confused what these vented caps are suppose to look like. My cap doesn’t say “vented” like the one Bill posted. But mine does have the yellowish looking filter like element on inside/bottom of the cap. Like Bill’s new cap, my cap also does NOT have a hole in the outside/top of the cap

1BA39199-1DD6-4157-B5A6-E50A7B4E47C2.thumb.jpeg.4dffe701cac3d6fe9b649186fc4bf6de.jpeg

 

 

 

I am assuming that is a check valve. It was on there when I bought it. If you look at the cap that is on my car now (NOS original) the first picture. You will see there is a hole right in the very center of the cap. The cap that I took off and no longer use (3rd & 4th Pictures) does not say vented either. You can have that cap for free if you want it. Just pay the postage, which I would assume would be 1st class.

 

Bill

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Bill,

  Your first 2 pics is what I have come to recognize as an original cap. The next 2 pics do not resemble an original cap.

  I think the cap which was on your car (the 2nd two pics) when you bought it is a replacement. It also appears the replacement was not a vented cap and someone drilled a hole to make it so.

  The bronze fitting at the end of the vent hose has been added, dont recall ever seeing such a fitting on any first gen cars I have owned.

Tom

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Google says a vented fuel cap allows small amounts of air into the fuel tank. It also says one way check valves will allow air out of the tank.


So I think I can get a check valve like Bill’s that allows air “out” (I’m sure a bit of fuel that gets trapped in the bottom/end of the loop in the hose leaks out along with the air too, it’s probably such a small amount that Bill doesn’t notice) & a vented cap that allows air “in” then I’ll be good?

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Water always seeks it's own level. Something we learned in general science in the 6th grade.   Could the same principle apply here?  If the top of the loop was lower than the level of gas in the tank, gas could find it's way up and out the loop. What if you made a loop that was higher than the top of the tank?

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Yes, u are correct. Earlier in this thread someone mentioned the 2nd Gen Rivi’s figured it out & added a steel tube going into the trunk.

 

In the 1st Gen’s we don’t have much room behind the license plate for a bigger loop than what u see in my pic. Well, at least not on the 65’s (can’t speak for 63/64’s). I might be able to get another inch or so. But the loop will start to flatten out or get horizontal. 


I main problem is with our non-baffled fuel tanks & the sloshing fuel at start & stops. There’s no way to prevent that. 
 

I will try to set myself car up with the check valve like Bill’s. That “should” work

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