Gasoline Evaporation "Tip"

[2nighthawks]

For what it's worth, I have solved a problem that I have experienced several times during a lifetime of Model T and Model A ownership. Not sure how many others have had similar "experiences", but I have had several instances whereby partial tankfuls of gasoline have COMPLETELY evaporated when a car was inadvertently left unused for a whole season (or longer) and slow as I am to "catch on", I have discovered a way to eliminate this problem. On several occasions during the last few years, I have let a "T" or an "A" set for several weeks before finally realizing that I will probably not be driving the car again for quite a period of time, like for instance, in the Fall, when I finally realize that the car will probably be left idle until at least the next Spring. Upon such "realization", I apply a little piece of tape (black plastic electrical tape works well) over the vent hole in the gas cap. Knowing my ever-failing memory now that I'm crowding age 80, I also stick a little piece of matching "reminder tape" on the steering wheel as a reminder for several months (or maybe longer) the next driving season. Here's what I have decided actually happens if you don't do this with a partial tank of gasoline:

One of the Model T's that I leave in a garage all winter is a perfect example of what I believe happens. The garage gets fairly warmer during the daytime, and considerably colder at night. This constant daily/nightly temperature change all winter long, causes the gasoline tank and the volume of air inside the partially empty (or partially full) gasoline tank to actually "breathe" (like inhale/exhale) thru' that tiny little vent hole, on a daily/nightly basis, all winter long. Believe it or not, a "several gallon" quantity of gasoline will completely evaporate over such a long period of time. I also believe that this also why some of us "T" owners have problems with the modern gasoline (which is "hydroscopic") causing the hard-starting problems that some of us have experienced.

I'm curious how many other folks have, at one time or another, experienced a partially full (or empty) tank of gasoline to completely and "mysteriously" completely disappear over a period of time,...????

As always, just my "opinion" of what actually happens and one way to prevent it,....for what it's worth,....harold

[Allan]

Harold, I have a different experience. Rather than volumes of pertrol disappearing through the cap vent hole, I have had weeping at the tank outlet and carburetor. The leaks are slow enough that the fuel evaporates before it gets a chance to drip, so the only indication is a slight stain at the leakage point.
Allan from down under.

[Norman Kling]

One of my cars (the same one each time) seemed to run down to an empty tank every time it was parked for a long time. I did two things which have helped. One is that I lapped in the valve at the sediment bulb and used some of the special grease you can get from the vendors and a new lead seal at the valve. I also replaced the needle and seat at the carburetor. I had the same problem, the leaks were so slight that I didn't realize it was going out. it is not like a modern car which has a fuel pump. With gravity flow, it just keeps flowing as long as there is even a small leak. I would be more concerned with water forming in the fuel from air going in and out of the weep hole because of the humidity and dew point which like the inside of cold windows, the inside of the tank will form water droplets which remain in the tank even when the air goes out.
Norm

[Dan B]

I'm curious how many other folks have, at one time or another, experienced a partially full (or empty) tank of gasoline to completely and "mysteriously" completely disappear over a period of time,...????

Hmm, that’s a new one.

[John Codman]

I agree with Danb. I would rather that the gasoline evaporate then turn into the crud that it does. I would drain the tank and use the fuel in a car that I am actually driving. In my case, I use old fuel mixed with new in my garden tractor.

[2nighthawks]

John C. - I agree, draining the tank is always the best idea, but you kinda' missed one of the points that I was trying to make,....is that once in awhile, you just sorta' get "caught", because the last time you drove the car, you didn't realize that THAT was gonna' be the last time for the year, because all of a sudden, several weeks, or a month has gone by, and so NOW, you know that you won't drive it any more until next Spring. That's about the time that I decide to block the gas cap vent hole with a piece of tape, and whatever gasoline is left in the tank will still be there next Spring, or Summer, or whenever! And like you and others have said, if won't turn into "WHATEVER" and/or it won't absorb water like the modern "gasohol" junk fuel does!

[2nighthawks]

One other thing that convinces me of how much gasoline can evaporate just because of the daily inhale/exhale of the gas tank thru' the vent hole because of temperature change, is something you reminded me of Norm:

Besides the Model T I talked about above, that's inside the garage about a hundred miles away from me all winter, I store another one inside an enclosed trailer. This one, I absolutely know is not leaking anywhere around the carburetor or fuel line connections, shut-off valve, etc, but every time I would open up that trailer, there was a strong smell of gasoline! Really, REALLY bothered me, as I remember how careful my Dad was about gas fumes in the bilge of a 30' ChrisCraft cabin cruiser he kept moored in Burnham Harbor in Chicago. Before starting the engine, he would always open the engine cover up first thing before anything else, and bend down and "sniff" the bilge area around the engine before starting the engine. (I remember that every once in awhile, you'd hear of a terrible explosion and fire on a boat where that precaution was not taken!)

Anyway, without doing absolutely anything else to that Model T in the enclosed trailer except putting a little piece of tape across the gas cap vent hole, since then, I have never once detected any smell at all of gasoline when I open up that trailer. So, for that reason, I'm convinced, and as our famous carburetor guy Stan Howe, says,....yer' mileage may very", ..... ....harold

[Michael Peternell]

My first thought is if it actually evaporated out of the tank it would be a lacquered up mess. Both tank and carb. IMHO.