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Old 06-13-2016, 11:08 PM   #687
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1977 20' Argosy 20
Arlington , Texas
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Martin,

Congratulations on retirement, I did that 4 years ago and now I don't have time to go to work - too many personal projects!

In regards to gas tanks. My 77 20 footer came from Chevrolet with a 24 gallon tank - far too small for cross country travel. Also by 1982 the factory tank had developed a crack along a crease in the bottom from an name brand after market locking gas cap that caused the tank to pressurize. The flexing cracked the metal and leaked. I had a custom 50 gallon tank made of steel with baffles and interior coating. Now in 2016 the tank interior is still clean and the "old" cap is still in place. The cap rubber gasket now has cracks in the rubber such that the tank can't develop pressure or vacuum.

Fortunately on the 77 20 footers the tank is just behind the left front wheel and can be readily lowered off the chassis.

Gregg
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Old 06-14-2016, 03:50 AM   #688
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Thanks Greg.

There certainly seems an issue whereby the size and type of the filler neck (1 3/8" and deep cam) is more normally found on vehicles with either non-EC (cap allows air in but not out) or EC (sealed cap) tanks, whereas the lack of vent tube in the tank itself means we need a full vented cap.

As soon as the volume of gas in the tank is left low enough that it can be heated by ambient conditions and so evaporate (more fuel reduces the effect) any modern aftermarket cap turns the tank into metal balloon. Unfortunately my original cap is long gone.

When you had the tank rebuilt did you add a separate vent line?
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Old 06-14-2016, 07:42 AM   #689
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1977 20' Argosy 20
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At the time (1982) of making the new tank, I didn't realize the issues on venting as I assumed that mine had the carbon canister vapor recovery venting system. As I was installing the new tank, I discovered that there was no venting at all; and I also experienced the pressure release as I removed the cap. For the time being I will continue to use the old Stant (brand) locking gas cap with the cracked rubber seal - which vents both in and out. I am considering getting a carbon canister vapor recovery system from a wrecking yard and installing that. The internal pressures can put pressures on the fuel pumps with unknown results.
Gregg
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Old 06-14-2016, 08:09 AM   #690
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1974 20' Argosy 20
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Quote:
Originally Posted by martin300662 View Post
But a normal person wouldn't spend a small ransom on one of these little beauties...
Point taken...!

Quote:
..anyway our A class Mercedes has a fuel gauge that reads left to right as it empties so I am sort of used to it!!!
I.e., backwards....kinda like driving on the wrong side of the road like you do across the pond?
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Old 06-14-2016, 09:00 AM   #691
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Originally Posted by martin300662 View Post
Thanks Greg.

There certainly seems an issue whereby the size and type of the filler neck (1 3/8" and deep cam) is more normally found on vehicles with either non-EC (cap allows air in but not out) or EC (sealed cap) tanks, whereas the lack of vent tube in the tank itself means we need a full vented cap.

As soon as the volume of gas in the tank is left low enough that it can be heated by ambient conditions and so evaporate (more fuel reduces the effect) any modern aftermarket cap turns the tank into metal balloon. Unfortunately my original cap is long gone.

When you had the tank rebuilt did you add a separate vent line?
Ok, now I see where your excess pressure is coming from. It's been a long time since I've thought fuel emissions systems!

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Originally Posted by GWallace View Post
At the time (1982) of making the new tank, I didn't realize the issues on venting as I assumed that mine had the carbon canister vapor recovery venting system. As I was installing the new tank, I discovered that there was no venting at all; and I also experienced the pressure release as I removed the cap. For the time being I will continue to use the old Stant (brand) locking gas cap with the cracked rubber seal - which vents both in and out. I am considering getting a carbon canister vapor recovery system from a wrecking yard and installing that. The internal pressures can put pressures on the fuel pumps with unknown results.
Gregg
Gregg, to retrofit a carbon canister system wouldn't you have to add a vent port in the top of your tank?

My tank is still being built at the fab shop and for some odd reason I had them add a spare 3/8" npt bung on top in the off chance I would want to vent the tank. Looks like I'll be using that bung after all!

I'm thinking about using this vent valve. The only tricky part is it's supposed to be mounted higher than the filler neck. That could get a little tricky unless I run the hose up into the front wheel well.
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Old 06-14-2016, 09:50 AM   #692
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Quote:
Originally Posted by GWallace View Post
At the time (1982) of making the new tank, I didn't realize the issues on venting as I assumed that mine had the carbon canister vapor recovery venting system. As I was installing the new tank, I discovered that there was no venting at all; and I also experienced the pressure release as I removed the cap. For the time being I will continue to use the old Stant (brand) locking gas cap with the cracked rubber seal - which vents both in and out. I am considering getting a carbon canister vapor recovery system from a wrecking yard and installing that. The internal pressures can put pressures on the fuel pumps with unknown results.
Gregg
Your description of a cracked rubber seal has given me a idea to try. Its sunny here and approx 80, and the tank is about 1/4 full so ideal conditions to experiment. I have a spare, new, non-EC cap (so vented in not out), removed the rubber seal and cut grooves across the sealing surface about half the depth of the rubber and radially every 1/8 of a rotation, so now there is a narrow gas path from inside to outside of the sealing surface. I will give it a few hours then see if the pressure has built at all.
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Old 06-15-2016, 07:48 PM   #693
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Your description of a cracked rubber seal has given me a idea to try. Its sunny here and approx 80, and the tank is about 1/4 full so ideal conditions to experiment. I have a spare, new, non-EC cap (so vented in not out), removed the rubber seal and cut grooves across the sealing surface about half the depth of the rubber and radially every 1/8 of a rotation, so now there is a narrow gas path from inside to outside of the sealing surface. I will give it a few hours then see if the pressure has built at all.
..... and the results are .....?
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Old 06-15-2016, 11:58 PM   #694
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I checked a couple times yesterday and had no pressure build up, but thought I was not really giving it a fair test, so left everything untouched until dusk today and had no pressure so maybe simply creating an airway from in to out across the gasket is enough?

Will have to test over a longer period to be sure.
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Old 06-16-2016, 01:10 PM   #695
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I checked a couple times yesterday and had no pressure build up, but thought I was not really giving it a fair test, so left everything untouched until dusk today and had no pressure so maybe simply creating an airway from in to out across the gasket is enough?

Will have to test over a longer period to be sure.
So the initial results are promising. After hearing of your issues I'm definitely going to add a vent to my new tank. I think there is room underneath the flapper door that covers the filler cap for a vent like this one.
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Old 06-16-2016, 01:26 PM   #696
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So the initial results are promising. After hearing of your issues I'm definitely going to add a vent to my new tank. I think there is room underneath the flapper door that covers the filler cap for a vent like this one.
Next time the tank come out I will do the same Brad; at the moment I am just trying to make the current issue not the reason for having to pull the tank.

I think this little drawing from the guys you linked to, is key



I actually have some space in the cavity between the outer skin and the wet room (accessible from the cassette toilet door) that would be an ideal location for a valve link that as it is directly above the tank, higher than the filler nozzle and can easily be inspected.
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Old 06-16-2016, 01:59 PM   #697
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Here's a picture that you previously posted of Bella's filler neck. I think the vent valve could be located where I placed the big red dot.
Click image for larger version

Name:	bella-filler-neck.jpg
Views:	24
Size:	138.1 KB
ID:	264588

If you still have access to that area that's have the battle won right there!
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Old 06-16-2016, 02:50 PM   #698
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Here's a picture that you previously posted of Bella's filler neck. I think the vent valve could be located where I placed the big red dot.
Attachment 264588

If you still have access to that area that's have the battle won right there!
I think I posted that image from one of the other guys rebuilds, either way that area is now behind the (very narrow) wardrobe and could only be accessed by removing the passenger side bed, and the wardrobe.

The cassette toilet is directly above the fuel tank but the walls of the wetroom are vertical and there is a gap of around 3in where a tube could come up from the tank through the floor and mount.



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Old 06-16-2016, 03:00 PM   #699
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Ah, I thought that was a picture from Bella.

I'm assuming you would then drill a hole in the outer skin for the vent to use?
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Old 06-16-2016, 03:27 PM   #700
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Ah, I thought that was a picture from Bella.

I'm assuming you would then drill a hole in the outer skin for the vent to use?
Hadn't really thought it through Brad - as I am hoping not to have to do it. Another 80 degree day here and again no pressure!
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