I have heard that you should keep your fuel tank as full as possible, to reduce the exposed surface on the interior of the tank, on which condensation (ie. water) can form.
Is there any truth to this?
Also, is it ever dangerous (other than the risk of spilling petrol in the process!) to fill up the tank completely, to just before where the cap goes? I'm referring to the tanks where this is physically possible, of course. In other words, is there ever any need for 'a bit of air in the system' ?
Actually, you are keeping =air= out of the tank, which carries moisture ( water vapor ) with it.
When the gas pump clicks OFF, that's it. No *topping up.* You need that extra air space in the tank to allow for expansion.
Lg
Filling to the level of the cap would be a bad idea for several reasons. If it's that close to the top any expansion will force fuel out the vents and be a hazzard. Even filling the tank beyond the automatic shut-off or so can cause emission system quirks and problems that may delay you from starting and can turn on indicator lights. Much of the fuel sold today already has alcohol added as an oxygenate and that will absorb some moisture. And running off the top half of the tank makes your in-tank electric pump's job easier, but you don't have to go crazy over filling.
"Lawrence_Glickman" wrote in message news: snipped-for-privacy@4ax.com...
Most gasoline tanks I am aware of include an extra isolated space to handle fuel expansion, either in the way the tank is shaped, or in a some cases, an actual add-on remote reservoir of some sort (my 1975 280Z had one of those). The only danger from over-filling the tank (aside from spilling gas on yourself, or the ground) is forcing gasoline into the charcol canister and saturating it with liquid gasoline. The "click-off" point for the automatic nozzles hardly means anything. As far as I can tell they are almost random. I've not had a car in ages that you could not add significanly more gas after the first "click off" point. Unless you stand there and spend a significant period of time dribbling gasoline into the tank, I don't think there is much risk of filling the tank so full that you need to worry about expansion of the fuel forcing gas out into the charcol cannister. The last car I owned where this was even a possible problem was a 1974 Jensen-Healey. The tank was mounted high between the passenger and luggage compartments, with a central filler neck. The neck went straight into the middle of the tank but included an internal lip of sorts that left an air gap of more than an inch between the lower edge of the filler pipe and the top surface of the tank. If you tried really hard, and jiggled the car a lot, you could add gas and partially fill the gap. But even then I never had any problem with forcing the fuel out into the cannister.
Ed
Very true.
The problem is that once the saturation limit is reached for moisture in the alcohol fraction, precipitation will occur. Not only will a large portion of the water settle out but it will bring a good bit of the alcohol out with it. At this point, it is very difficult to put the wet alcohol and gasoline back together again.
A good dispersant can be a helpful additive to gasoline, especially during the colder winter months and in high humidity situations. A lot of additives are based on alcohols alone, but the better ones contain surfactants which help keep any moisture moving.
Condensation isn't a worry in hot weather. I don't bother to fill the tank full in summer. But since I don't drive the car much in winter I fill the tank in the fall when we start to get frost (condensation) and keep it filled until spring.
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Some places condensation can be a problem even in summer, but is usually much worse in winter. When the water freezes and clogs the filters, lines, etc, it can really be a PITA, since it is too late to get the 'chemical' to the spot where it is needed. Alcohol in the fuel has solved a lot of that sort of problem, although there are still places where it is not used.
defintely a problem in marine fuel tanks. We actually employ fuel separators to keep the water in a separate bowl.
If your in a warm climate, I wouldnt worry too much but there's truth to it. Its severity varies.
my .02
Absolutely. We used to provide chemical inhibitors for those situations, ed, to keep bacteria, mold, etc depressed in the wet fuel. Chemical treatment and the use of water separators could prevent trouble.
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