Gas Tank Vent Mod

M

MikeB

Active member
Dec 24, 2018
288
29
28
Lower Alabama
I’m currently doing a total fuel system update. The PO used the existing hard vent line to vent just the main tank and ran a separate 7/16” hose
from Aux tank to a “T” fitting into the small length of hose just below fuel filler. I suppose this was to allow for faster fill ups. I’m
thinking of going back to a single line branching to each tank like factory. Any find this mod beneficial?

Thanks
--
M Beam
75’ Avion
TBI EBL , 3.70 LSD and other stuff
Zuki Sidekick,
Dozier Al
 
That was a suggested modification a few years back, although I haven't heard much about it lately. If there are no bellies or dips in the vent line,
it might be a better system than the original set-up. As long as the added vent line doesn't hold gas in it anywhere, it would theoretically vent the
tank more efficiently than the factory system.

The original venting works well if it is in good original operating condition, but I can see where separate vent lines, to a tee, as you've described
might work better. With mine in the stock configuration, I can fill the tanks easily up to the point where the gas starts to burble in the filler
neck, then I have to wait 30 seconds to a minute before slowly topping it off, sometimes with as much as an additional 5 - 10 gallons.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member
 
> I’m currently doing a total fuel system update. The PO used the existing hard vent line to vent just the main tank and ran a separate 7/16”
> hose from Aux tank to a “T” fitting into the small length of hose just below fuel filler. I suppose this was to allow for faster fill ups. I’m
> thinking of going back to a single line branching to each tank like factory. Any find this mod beneficial?
>
> Thanks

Mike,

Search for Recommending High T.

It is the result of a CFD analysis that I did years ago.

Matt
--
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
 
> > I’m currently doing a total fuel system update. The PO used the existing hard vent line to vent just the main tank and ran a separate
> > 7/16” hose from Aux tank to a “T” fitting into the small length of hose just below fuel filler. I suppose this was to allow for faster fill
> > ups. I’m thinking of going back to a single line branching to each tank like factory. Any find this mod beneficial?
> >
> > Thanks
>
> Mike,
>
> Search for Recommending High T.
>
> It is the result of a CFD analysis that I did years ago.
>
> Matt

I should have known. My PO has done some pretty good mods. This statement from your post clears it up. “ because the rear (main) tank actually
fills first (with little regard to vehicle trim (ride height front to back), it will always flood the vent line if given the opportunity”.

I’ll be replacing the High T.

Thanks
--
M Beam
75’ Avion
TBI EBL , 3.70 LSD and other stuff
Zuki Sidekick,
Dozier Al
 
We have done at least two coaches a month in the lat 20 years and found
that if done right, the filling of the taks are fast and reliable.
I have not seen Matt's mod so I do not understand how that works.
We like to do things in a way other GMC shops can follow.

> > > I’m currently doing a total fuel system update. The PO used the
> existing hard vent line to vent just the main tank and ran a separate
> > > 7/16” hose from Aux tank to a “T” fitting into the small length of
> hose just below fuel filler. I suppose this was to allow for faster fill
> > > ups. I’m thinking of going back to a single line branching to each
> tank like factory. Any find this mod beneficial?
> > >
> > > Thanks
> >
> > Mike,
> >
> > Search for Recommending High T.
> >
> > It is the result of a CFD analysis that I did years ago.
> >
> > Matt
>
> I should have known. My PO has done some pretty good mods. This statement
> from your post clears it up. “ because the rear (main) tank actually
> fills first (with little regard to vehicle trim (ride height front to
> back), it will always flood the vent line if given the opportunity”.
>
> I’ll be replacing the High T.
>
> Thanks
> --
> M Beam
> 75’ Avion
> TBI EBL , 3.70 LSD and other stuff
> Zuki Sidekick,
> Dozier Al
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>

--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk
http://www.gmcrvparts.com
1-800-752-7502
 
Not sure why you wouldn't want the separate Aux tank vent line. Seems to me it may help venting and wouldn't hinder it at all. When I did my tanks a
year or so ago, I did the 'High T' mod. I was under there recently and tied up a few places where it dipped a quarter inch or so on its way forward.

--
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid
November 2015.
 
I just completed the "High "Y" mod. I used Stainless straight tubing, .065 wall thickness and a brass "Y" fitting that had a 1/2" barb on one side. I
found the Brass "Y" fitting on Ebay. I wanted to make sure there was no pooling of fuel in the line. I can't comment on its effectiveness, but by all
accounts it should vent each tank separately until the bottom of the cockpit floor and just before the 1/2" OEM tube at the gas fill.
--
Tom & Oki Katzenberger,
Kingsville, Maryland,
1977 23' Birchaven, 455 C.I.D.
 
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