OT - automotive fuel filling - how does the gas station pump fill nozzle sense a full tank?

I have two vehicles that have fuel filling issues. On my 61 Falcon, I have to pump the fuel in very slowly or else it will splash back out
of the fill port (I do not remember this as an issue when I first started driving this car back in the late '70s but I had the vehicle out of service for a decade and when reinstated in '03 this was an issue - I suspect that fuel delivery volume and/or pressure increased over the years). On my '91 F150 the rear tank does not accept more that 3/4 tank capacity. On the older vehicle, there is a single large (about 2.0 in. ID filler hose between the fill port and the tank. On the F150, there are dual hoses. The inner fuel hose that transport the fuel from the fill port to the tank is 1 in. ID. THe inner hose is routed inside of the larger (about 2.0 inch ID) that appears to function as the vent hose. If I better understood how the gas pump nozzle sensed a full tank, I could proceed with changes to both vehicles.
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snipped-for-privacy@c3net.net wrote:

The 61 system is a simple single line fill. The problem there is likely the way the tank sits and the location of the fill pipe on the tank.
On the 91 you have one fill line (the inner tube) and a vapor vent line (outer tube)
Nothing you can really change on either vehicle unless you want to replace most of the fuel tank parts to get the fill pipe higher on the tank and relocate the fill neck as well.
The F-150 problem could be the line being crushed between the frame and box. See this a lot on trucks when the box mounts start to rot.
--
Steve W.

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mattathayde had written this in response to http://polytechforum.com/metalworking/ot-automotive-fuel-filling-how-does-the-gas-station-pump-208535-.htm :
------------------------------------- snipped-for-privacy@c3net.net wrote:

one issue i saw on a jeep forum was the roll over valve had gotten stuck in a weird position and made it fill very slowly. that could be an issue too. i did notice on my jeep cherokee that some places i cannot put the nozzle in al the way
-matt
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I find your query amazing. Why would you think the readers of this or any newsgroup could tell you what is going on with your vehicles better than you. Please look yourself.... it isn't rocket science. Furthermore, no vehicle would ship from the factory with those faults. So, instead of trying to modify the original design, perhaps you should just take things apart and fix the problem. Steve

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On Mon, 16 Nov 2009 17:16:11 +0100, "Steve Lusardi"

Blink blink...blink.
Not having a good day Steve?
Sorry to hear about that.
Gunner

"Aren't cats Libertarian? They just want to be left alone. I think our dog is a Democrat, as he is always looking for a handout" Unknown Usnet Poster
Heh, heh, I'm pretty sure my dog is a liberal - he has no balls. Keyton
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http://www.wonderquest.com/sleeping-birds-gas-nozzles-cold-hospitals.htm
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snipped-for-privacy@c3net.net wrote:

Sounds like a clogged tank vent to me.
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On Mon, 16 Nov 2009 13:13:49 -0600, the infamous RBnDFW

Yeah, clogged vent, or too fine of a strainer in the fill hose. Anti-siphon devices can cause these problems.
-- When we are planning for posterity, we ought to remember that virtue is not hereditary. -- Thomas Paine
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On Sun, 15 Nov 2009 18:42:19 -0800 (PST), snipped-for-privacy@c3net.net wrote:

The automatic shutoff nozzles have a little water-wheel style pump in them pushed by the outgoing fuel to provide power for the shutoff system. There is a little sense vacuum fitting on the bottom tip of the nozzle that sucks fumes back through the pump and to the vapor recovery hose in recovery areas, or puts it back in the oputgoing fuel stream on non-emissions pumps.
When that little sense port sucks in liquid fuel instead of vapors, the little turbine pump stops and trips off the nozzle.
The new emissions nozzles are shorter because of the vapor recovery seal sleeve, and far more sensitive to any fuel splashes getting sucked in to avoid any spills - so if your gas filler neck on the car is too close to horizontal, or has a bend too close to the fill end, and any fuel splashes back at all, the new nozzles trip out.
The usual solution for this is putting the nozzle in "upside down" so the sense hole is on the top, makes it a little less sensitive - but then you increase the odds of a small spill when the tank is full.
And since the stations can get fined for any sort of spill, every time the attendant sees you "doing it wrong!" they will stop you and/or turn off the pump on you. So you always do this trick with your car parked with your filler out of view of the attendant. Or you have to stand there and explain the whole thing to them. Every. Single. Time.
Been there, Done that, got rid of my 62 Scout partly because of this. Dual tanks meant you had to go through the same mess twice. Or get out the gas can and fill the car 5 gallons at a time - Into the can, then into the car, Into the can, then into the car...
--<< Bruce >>--
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Steve L: why bother to reply when you have no usefull information?
To the rest of you thanks for the suggestions (esp Rick for the link). On the F150 (still relatively new to me, bought in late June w/ a deadpump in the rear tank) I never filled the tank prior to replacing the fuel pump. The inner fill tube appeared to be quite long (extending down into the tank quite a ways) but since I had never taken apart a "modern" fuel system, I just excepted it as normal - now I understand why that tank will not accept the last 4+ gallons of fuel.
On the Falcon, fuel splash back has become a universal problem for all owners of these vehicles. The fuel fill opeing is 7.5 inches above the upper surface of the gas tank and the fill pipe makes a sharp 90 degree bend. Many owners install a fuel inlet pipe and cap from a '60 or early 70s pickup so that the fill pipe is straight up inside of the trunk. I am not willing to open the truck just to fill the tank and am quite concerned about a fuel spill INSIDE of the trunk during refilling. Lately, some people have had some success with retrofitting a modern tube in a tube fuel filler system from a later vehicle (that would be actual metal working to make such a system fit the opening). I did not want to go this route until I better understood how the fuel pump nozzle worked and why some are having great success and others are not having as much success.
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On Mon, 23 Nov 2009 04:43:22 -0800 (PST), snipped-for-privacy@c3net.net wrote:

Do NOT try to defeat that filler-tube extension that sticks down into the fuel tank! It is there for a reason - They have to leave expansion space, or you fill the tank with cold gasoline and park in the sun, and soon you have a gasoline geyser as the tank overflows. One spark in a decent combustible air-fuel mix, and...
If the cap doesn't allow the liquid fuel to escape, the overflow of the tank forces liquid gasoline into the carbon cannister and wrecks it on newer cars with evaporative emissions systems - that kills the vapor recovery system and costs you $500 or more to get fixed. Obviously, that isn't a good option either.

That 90-degree bend in the fill neck, and/or the very low fall angle found on the rear-bumper style fill necks, is what kills you - any turbulence in the fill neck causes fuel to splash back toward the cap, and the 'tank full sensor' on the fill nozzle is deliberately set very sensitive to avoid spills.
They changed the nozzles when they retrofitted all the gas pumps for vapor recovery and lessen the chance of spills, and effectively broke them for older cars.
It's one of those "Sucks to be you!" things. :-P
Detroit wants you to junk the antique and buy a new car, of course. So even if their official letter says "Sorry, there's nothing we can do to help you..." they are cheering on the inside.

There's also the problem of having a *VENTED* fuel cap (most caps on older cars are) inside a closed trunk - a sure recipe for disaster.
If you drive the car enough where you are willing to sacrifice looks for utility, go straight up and cut a hole, put the gas cap on the apron in front of the trunk lid like a Jaguar XK.
You could steal a recessed gas door and pocket off a car that has the proper curve on the door, mount it on that trunk apron, and plumb a drain line from the pocket through the trunk to under the car to channel away rain water and any fuel spills. But that's going to be a LOT of complex custom body work.

You might contact the folks at Gilbarco or Husky who make the nozzles, and see if they have any "Suggested Design Standards" that they follow while designing their nozzles. Might give you some insight into the problem.
If nothing else, you might be able to make a short plug-in "extension" that is a slip-fit inside the existing fill neck on the car, to get the nozzle tip out of the turbulence zone. It will need a collar or rim on the outer end to fake the gas-cap latch lip for the hold-in spring on the nozzle tip, and make a seal on the new Stage II and Stage III vapor recovery nozzles. And it needs to be metal to avoid any static charge problems.
Don't make an extension any longer than you absolutely have to in order to solve the fill problem, because it will make it way too easy to overfill the tank. And remember that the State Fire Marshall and/or the Air Quality Management District will have kittens if your gadget causes spills. Spills pollute, and turn into fires way too easy.
--<< Bruce >>--
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What's that Lassie? You say that Bruce L. Bergman fell down the old rec.crafts.metalworking mine and will die if we don't mount a rescue by Mon, 23 Nov 2009 22:09:25 -0800:

Maybe you can. I know Jeep Wranglers(others?) had a 20 gallon optional fuel tank(15 gallon standard). The larger tank was just removing the filler extension in the tank. Still leaves the required expansion room, but allows the extra 5 gallons of fuel.
--

Dan H.
northshore MA.
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On Wed, 25 Nov 2009 00:27:07 GMT, snipped-for-privacy@privacy.net (dan) wrote:

I've seen that system, and it is a different tank. The factory tank is the standard two-piece stamped terne-plate steel welded at the flat seam. There's a lot of wasted space between tank and body, and the tank and it's little skid plate.
The extra capacity tank is welded plate steel shaped to fill every spare inch of the cavity. And it is not cheap, because they are hand-made, and they had to submit samples (and a Jeep) for emissions testing to prove the evaporative emissions systems still works properly.
--<< Bruce >>--
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What year(s)? The 5 gallon fix was posted on the Jeep group, and many forums. I'm sure they changed designs over the years. Mine had the 20 gallon tank from the factory ('99 wrangler) and the tank was the standard two halves welded at the horizontal seam. If you had the 4 cyl. instead of the 6 cyl. you got the tube that limited it to a 15 gallon fill.
--

Dan H.
northshore MA.
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