Gas Cap - new cars still have them ?

Atlanta_man

Atlanta_man

New member
I rented a 2008 Ford Explorer last week and went to gas it up. Manual gas door panel in the usual location over the back wheel.

No gas cap. It has a sign under where one should be that says 'no gas cap'. Just stuff the pump nozzle in past the little metal door and gas up !
 
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No way that would pass inspection in large cities around this country. Hell, even the small counties in Texas run a vacuum test on the gas cap as a minimum....and we all know how relaxed the inspection regulations are in Texas!

That sounds like the rental car company lost it and decided not to replace it with a new one.

This note didn't happen to be hand written, did it??:D ;):
 
Doesn't matter big city/podunk town.. FEDERAL emissions laws regulate evaporative emissions, that's why cars have charcoal canisters to absorb evaporation while the car's not running. The fuel system is sealed, basically. That's also why a loose gas cap will throw a check engine light on many newer cars.

Although I could imagine they have a spring loaded flapper valve on there, I rather doubt that would be reliable enough.
 
it's a Ford, of course its not reliable enough.

Being a fire investigator, i constantly get called to Ford fires all the time from their cruise control switch staying activated always. But anyway, never heard or that, i would still want some kind of a gas cap.
 
cut-and-paste from msnbc site:

updated 6:01 p.m. ET, Wed., Jan. 6, 2008
DETROIT - For those drivers who pull away from the pump with their gas tank cap on the trunk lid, Ford Motor Co. has begun to make good on a 2006 promise to get rid of the caps on its entire model lineup.

Jettisoning the pesky caps will become most apparent in the new 2009 F-150 pickup truck, Ford's top-selling vehicle, which was unveiled this week at the North American International Auto Show. It will hit showrooms in the fall.

The capless refueling system already is available on the 2008 Ford Explorer sport utility vehicle, and it's coming to the 2009 Flex crossover and Lincoln MKS luxury sedan, said Matt O'Leary, chief engineer on the pickup.
 
Wow, I wonder how they plan to get them to pass inspection since those cars will be leaking gas fumes. Some drivers might get a surprise when starting their cars after it has been sitting in the garage for a while.

BTW, I cant believe that people are still setting their cars on fire with that cruise control switch from ford....didn't they recall that about 5 years ago?
 
It wouldn't be too hard. The check valve/flap will hold the liquid and any fugitive emissions could be stopped by a properly sealed gas door that was designed for vac conditions. This would be the equivalent of having a gas cap assuming when you drive away the gas door is closed.
 
If you use a door that would allow you to easily insert the gas nozzle, then this flap would need to open inward (toward the filler tube). If the flap opened in this manner, when you reduced the pressure in the lines, the flap would open. How would this work.

Does the OP still have the car? Can you snap a pic?
 
returned it already... btw the external gas door itself did have a gasket around it

in from the edge, not visible from the outside and the door did close flush with the body panel
 
Well, maybe that is how they keep the fumes from leaking. Although, I would image there would still be some leakage through the door when the pump was not running...
 
JeremyH said:
Well, maybe that is how they keep the fumes from leaking. Although, I would image there would still be some leakage through the door when the pump was not running...
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There shouldn't be any leakage. When you are operating the vehicle there would be a net neg pressure in the fuel tank area compared with atmosphere (an extremely small delta), allowing the air outside to hold the door shut. Any expected leakage should be from the atmosphere to the fuel tank, not the other way around.

When the vehicle is not running, I doubt there would be any significant emissions to warrant a concern. The seal can easily be designed (and I am fairly certain it is) to hold pressure. Think about an old mason type jar
 
shuly said:
There shouldn't be any leakage. When you are operating the vehicle there would be a net neg pressure in the fuel tank area compared with atmosphere (an extremely small delta), allowing the air outside to hold the door shut. Any expected leakage should be from the atmosphere to the fuel tank, not the other way around.
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Yeah, that is what I described above.

When the vehicle is not running, I doubt there would be any significant emissions to warrant a concern. The seal can easily be designed (and I am fairly certain it is) to hold pressure. Think about an old mason type jar
Click to expand...
 
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JeremyH said:
I would still think that the loss of negative pressure would allow gas vapors to be released.
Click to expand...

OK...guess its time for a quick physics lesson. Sorry I am an engineer so...:nerd:

If you have ever taken a physics course or even a lot of chemistry courses they cover this stuff with some fairly impressive examples. The core of the issue is TOTAL fluid energy. Fluids can be gases, liquids, supercritical fluids...

It is all about energy. If there is a potential difference between two fluids they will tend to reach equilibrium such that there is no net energy difference. Higher energy will move to lower energy. Typically with fluids such as gases and liquids we think of static pressure as being the primary difference in energy. This is not technically correct, but for the most part this type of thinking works fine, as it does in this example.

Say you have a rigid box divided in half with a gas on one side at 20 psi (higher energy) and on the other side at 10 psi (lower energy). Now say there is a small door between the two of them keeping them completely isolated from one another. The side kept at 20 psi is the side holding the door closed. (assuming it is hinged like a gas tank door)

Now take this analogy to your gas tank. There is a slight negative pressure inside the tank we are talking very slight. However, this is still enough to keep the outside air holding the door to the gas tank snugly shut. This will work as long as the gasket around the door continues to provide seal.

I wonder how this will affect vehicle inspections. Will they simply do away with the gas cap test, or will it be now placed on the door?
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You can check the door with a hydrocarbon sniffer...no problem to do for smog. If it were leaking, I imagine your check engine light would turn on due to the vacuum system not working correctly. Similarly if there is an issue with the smog/vac system now the check engine light is supposed to come on. Anyway, this should happen long before you ever smog the vehicle.

I still don't understand the reason for this. My first vehicle had a loose gas cap (not attached to the vehicle) and I never lost it. Now all of my vehicles have a cable attached to the cap and the vehicle. How are people losing these things?!?!
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:iagree: I have never lost my gas caps either.
 
No need for a lesson in physics (I have a Masters in the subject and am employed as a nuclear physicist).

I understand that there is lower pressure on the fuel system side of the door and why the door is kept shut when the vehicle is running, but that negative pressure is created by the fuel pump, which does not run when the vehicle is off. When the vehicle is off, the two sides should attempt to reach equilibruim. All of this also assumes that the gasket would remain in good condition over the lifetime of the car.

I have owned a few cars and none of them have ever had a failure with the gas cap....I have had gaskets and seals fail.

This seems like a bad decision for automakers....
 
JeremyH said:
No need for a lesson in physics (I have a Masters in the subject and am employed as a nuclear physicist).

I understand that there is lower pressure on the fuel system side of the door and why the door is kept shut when the vehicle is running, but that negative pressure is created by the fuel pump, which does not run when the vehicle is off. When the vehicle is off, the two sides should attempt to reach equilibruim. All of this also assumes that the gasket would remain in good condition over the lifetime of the car.

I have owned a few cars and none of them have ever had a failure with the gas cap....I have had gaskets and seals fail.

This seems like a bad decision for automakers....
Click to expand...

Ok ... then wouldn't you agree that the seal on a gas cap and the seal around a latching door albiet different sizes are doing the same thing once you turn off the vehicle? If they weren't eventually the gas tank would be crushed under those forces...

I am of the opinion that it would be more likely to need to replace the gasket around the door during some sort of regular interval 50k-75k or something. But wouldn't you agree it is doing the same thing as a standard gas cap?
 
Well, the seal on a regular gas cap is being made because the cap is screwed down to the fuel filler tube...not simply hoping that the pressure on the fuel side will remain lower. What happens if the gas temperature rises for some reason? Ideal gas law would indicate that the pressure would increase as well...
 
When you look at it to gas up it looks just like any other gas hole with the nozzle size restriction for unleaded spouts but it also has a shiny flapper door that opens out of the way when you stuff the nozzle in. Considerable spring pressure too - got to jam the nozzle in with authority.

Can't believe you guys with physics degrees are debating this without seeing a schematic of all the vapor recovery piping, pumps and the excess pressurized fuel flow return that people with engineering degrees designed. There's more to analyze than just a fuel pump and fuel cap / door.

Oh, I've got a masters in physics too ! So I will be quiet now...
 
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