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Fuel Evaporating?
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RailBoy
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PostPosted: Sat Jun 29, 2019 10:49 am    Post subject: Fuel Evaporating? Reply with quote

Hey Peeps out there, have a question for I think I ran across this a few times over the summers of the past 9 years owning my 74 VW Super Beetle...

Have any of ya'll experienced a fuel smell near or at the front of your bugs, being Supers or Standards when the temps are over 90+ degrees outside in summer?

See, I did today. Thing is it is outside and a Faculty Gloss Black Super. Thing is it is outside in direct sunlight, so wonder if this is heating up the tank thus evaporating fuel?

Why do I say this, well I had the Super in a garage up until two weeks ago, and inside temps there were hitting 90 degrees for there is no climate control.. I had a full tank of fuel in it 3 weeks prior to then. So, I jumped in the car one morning and basically did a 92 mile drive with it, all back roads with 55 mph zones, thus maybe seeing 60 mph. Usually it will get 22.5ish mile per gallon. Engine is a 2180.

On this trip the roads were no different than before were I get the 22.5ish mpg, but this trip, which was like 78 degrees out, I got what I calculated to be 20.8 mpg after the trip and did my fill up..

So, that is roughly lets say a 2 mpg difference in the calculations when doing mpg.

So, did I have fuel evaporating out of the tank when the car sat in the garage when it was seeing 90+ degrees temps at the beginning of summer here in Va.?

Thus, this gas smell I smelt today when walking by the Super at 1:30pm in 93 degree temps at the front of it is gas just evaporating out?

I do have all the factory evaporating stuff and correct hoses on. All new as well..

So, what is ya'lls take on this missing like 2 mpg different in this last trip plus smell in the summer heat? A norm of bugs?

Yea, just a pondering thought? I am getting ready to run it like 80 miles one way for the 4th of July week and will be driving, oh and by the way, my fuel gauge is not accurate like most peoples, I use a GPS and do mileage trips and gallon calculations to keep fuel levels in check..

Ok, hope ya'll are having a good day, maybe some Cali Folk or Arizona peeps will chime in and see what y'all have seen? Thanks again, just don't want to run out of fuel, lol.. RB
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Tim Donahoe
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PostPosted: Sat Jun 29, 2019 1:45 pm    Post subject: Re: Fuel Evaporating? Reply with quote

Fuel cannot evaporate from a closed system. You have vapors leaking from one, or a number of, rubber hoses, going to or from your tank, or a fuel leak, or a sender seal leak, or fuel cap seal.

Most likely, your fuel vapor hoses that go from the tank to the expansion chamber are responsible.

I’d pull (actually, I did) the tank and replace every single hose, including the filler hose. Also, check that the expansion chamber is air tight.

Tim
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viiking
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PostPosted: Sat Jun 29, 2019 2:42 pm    Post subject: Re: Fuel Evaporating? Reply with quote

Yes you should check your fuel system for leaks however your mpg difference could just simply be due to difference in how you drove the car over the distance on a particular day, tire pressures, day temperature affecting combustion efficiency. A whole myriad of things could give you the small difference.

I assume you top up the tank to determine the fuel consumption. Even topping up at different times of the day will give different volumes due to change in density of the fuel.
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RailBoy
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PostPosted: Sat Jun 29, 2019 3:56 pm    Post subject: Re: Fuel Evaporating? Reply with quote

Thanks guys for the reply, thought of all this but did just wonder if it was a nature of a VW Bug?

Happy 4th... RB
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bluebus86
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PostPosted: Sat Jun 29, 2019 4:54 pm    Post subject: Re: Fuel Evaporating? Reply with quote

Gasoline volume changes roughly 1% for every 10C change. underground storage tanks may contain 50F gasoline, that cool gas can give you an extra 2% or so on an approx. 90F day, just under a quart more fuel out of 10 gallons!

so if you fill a near empty tank on a hot day to the top, from a cool underground tank, verses topping off a near full tank that had been heated by the hot day, you will get about one quart more into the tank that was near empty, verses the tank that was near full, even if the fuel level you top off to is identical.

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viiking
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PostPosted: Sat Jun 29, 2019 5:17 pm    Post subject: Re: Fuel Evaporating? Reply with quote

^^^ This!.

It also makes you wonder how the gasoline pump delivery calculates. Using a Mass Flow Meter would compensate for temperature and density, but I doubt bowsers are fitted with anything as sophisticated.

A recent study in Australia found 4.8% of bowsers were underdelivering the amount of fuel and 1.6% overdelivering. This had doubled in the past year. The tolerance was +/- 0.3%. I'm sure a US study would be no different. It all relies on the capability and frequency of the calibrating technician.

So always fill up at night from a cold tank and never after a delivery if the day has been hot and the fuel in the tanker has been subjected to heat during the drive. The latter may be hard to determine, but avoid a gas station that has a delivery truck in place.

As previously indicated your actual fuel consumption difference is something like 8%. The methods you are using to determine are probably inaccurate due to the car's performance not necessarily the amount of fuel used, but still an interesting study.

As noted, do a thorough inspection of all of the systems. It may save a fire rather than a few dollars in fuel.
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RailBoy
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PostPosted: Sun Jun 30, 2019 11:40 am    Post subject: Re: Fuel Evaporating? Reply with quote

Thanks guys for the replys, see, I can see the fuel economy change, that makes since as well. Driving habits. But have seen up to 28 mpg out of this engine in a 60mph zone basically for 150 miles.... Yea, straight shoot of a trip, and the engine purred.

On the back roads as it was said, the something like 2 mpg difference can be numerous things. But what made me incline about the fuel smell led me to think it was also included into this calculation or the 2 mpg thing.

So, just saying, the nature of the beast is that the fuel system of the VW bug is a closed system, gotcha. On the up and up I have a new tank, all new hoses through out.

Maybe it was just me that day walking by the car on the 90+ degree hot day, just being overly sensitive that there was a smell, lol.. RB
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bluebus86
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PostPosted: Sun Jun 30, 2019 1:14 pm    Post subject: Re: Fuel Evaporating? Reply with quote

RailBoy wrote:
Thanks guys for the replys, see, I can see the fuel economy change, that makes since as well. Driving habits. But have seen up to 28 mpg out of this engine in a 60mph zone basically for 150 miles.... Yea, straight shoot of a trip, and the engine purred.

On the back roads as it was said, the something like 2 mpg difference can be numerous things. But what made me incline about the fuel smell led me to think it was also included into this calculation or the 2 mpg thing.

So, just saying, the nature of the beast is that the fuel system of the VW bug is a closed system, gotcha. On the up and up I have a new tank, all new hoses through out.

Maybe it was just me that day walking by the car on the 90+ degree hot day, just being overly sensitive that there was a smell, lol.. RB


the fuel system is not a closed system. Late Bug have charcoal recovery cans to minimize escaping odors, by collecting them when engine off, then when engine is running, the charcoal can is purged to the intake system.
If the system was closed, the car would cease to run as a vacuum is created by the displaced fuel being consumed by the engine.

older bugs simply vented to air, with no charcoal recovery system. Both types are open to the air however, not closed.

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Last edited by bluebus86 on Sun Jun 30, 2019 1:31 pm; edited 1 time in total
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Tim Donahoe
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PostPosted: Sun Jun 30, 2019 1:23 pm    Post subject: Re: Fuel Evaporating? Reply with quote

Blue, when I mentioned a “closed” system, I included the evap system in my meaning. “Closed” to me means that no fumes are escaping into the atmosphere, which an intact evap system accomplishes.

Tim
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PostPosted: Sun Jun 30, 2019 1:35 pm    Post subject: Re: Fuel Evaporating? Reply with quote

ok, so long as that is clarified. Closed to fumes, but not closed to air. Some folks may not understand what you know, But now they do !

Bug On! Smelling Good!
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PostPosted: Sun Jun 30, 2019 1:48 pm    Post subject: Re: Fuel Evaporating? Reply with quote

viiking wrote:
^^^ This!.

It also makes you wonder how the gasoline pump delivery calculates. Using a Mass Flow Meter would compensate for temperature and density, but I doubt bowsers are fitted with anything as sophisticated.

A recent study in Australia found 4.8% of bowsers were underdelivering the amount of fuel and 1.6% overdelivering. This had doubled in the past year. The tolerance was +/- 0.3%. I'm sure a US study would be no different. It all relies on the capability and frequency of the calibrating technician.

So always fill up at night from a cold tank and never after a delivery if the day has been hot and the fuel in the tanker has been subjected to heat during the drive. The latter may be hard to determine, but avoid a gas station that has a delivery truck in place.

As previously indicated your actual fuel consumption difference is something like 8%. The methods you are using to determine are probably inaccurate due to the car's performance not necessarily the amount of fuel used, but still an interesting study.

As noted, do a thorough inspection of all of the systems. It may save a fire rather than a few dollars in fuel.


A gov agency is out checking the accuracy of the pumps around here in Cali regularly . I’m guessing a bowser is a pump?
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Volks Wagen
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PostPosted: Sun Jun 30, 2019 5:19 pm    Post subject: Re: Fuel Evaporating? Reply with quote

dirtkeeper wrote:
I’m guessing a bowser is a pump?


In my world, a bowser is a mobile tank, like a mobile fuel tank in this case. So a fuel tanker. I'd say that's what Crocodile Dundee is on about too.
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