In ye olden times, we kept our gas tanks full to keep out air and therefore condensation. I have retained this habit. However, I am rethinking it. I have a
Tahoe with a big gas tank, and I don’t drive it much, maybe 2000 miles a year. I’m thinking the gas will get “old”, and this may be a bigger
problem than condensation–what with modern sealed tanks with pressure caps. If I kept it around half full, the gas that’s in there would be
fresher all the time. Any informed comments on this?
You can use fuel stabalizer. Ethanol in fuel absorbs water even more than gas. I would keep it full and run it out every few months.
In the old days tanks were vented directly to the outside world. As the tank breathed in and out, it would draw in moisture along with the air, and if the temperature outside dropped the metal could be come cooler than the gas. As the tank air, warmer than the outside air and potentially high in moisture (warm air holds more moisture suspended) chilled as the heat energy propgated through the tank’s metal, that “boundry layer” would potentially deposit its moisture on the inside surface of the tank as condensation. It would coalesce, drip down the side, and under the gas (water is heavier than gas…gas floats).
Now, recognize that pumps draw from the lower portion of the gas pool. Down where the water goes. Recognize also that cars used to use carbs, which operate on very low pressures and which pull the gas into the venturi, creating low pressures in some of the paths. Really old cars even used mechanical fuel pumps driven by the crankshaft that pulled gas through the line, making the entire line low pressure. In these low pressure areas the water vapors could form ice crystals…leading to the much demeaned “gas line freezeup”.
A lot has changed.
Firstly, today’s tanks breath in through a carbon filter. While the carbon’s purpose is to capture hydrocarbon molecules, it also catches some water vapor, reducing the amount of water vapor getting drawn into the tank. The charcoal is “activated”, which means it was soaked in acid to make it highly pourous. High porosity means greater surface area per given charcoal granule, and thus greater abillity for hydrocarbon molecules to stick to it. It also makes it more prone to capturing moisture.
Secondly, todays fuel delivery systems maintain a high pressure (40psi or more) throughout an entirely closed system, from the pump to the injector tip. There is no air whatsoever in the delivery and metering system to hold moisture, and no low pressure areas to allow crystallization.
Thus, the old concerns of water in the tank have been largely banished. But letting the gas sit for long periods still carries with it problems with degradation of the gas that prompt me to recommend against it…even if water isn’t a concern anymore.
I fill my tank if the prices are “low.” I paid $3.15 a gallon last week and filled up. Today I paid $3.59 and bought 10 gallons.
Yeah, wholesale crude and gasoline prices are skyrocketing over fears the Suez Canal could be closed due to mid-east unrest…
Todays sealed fuel systems are pretty much immune to moisture and condensation…The natural vapor pressure of the gasoline keeps the tank at positive pressure…
I was under the impression that tanks will still “breath” IE. A car is parked outside, its a high of 90, the tank vents pressure thru the charcoal canister, then at night when its 60-65 the tank develops a slight vacuum due to the contents cooling off, and admits air via the vent solenoid. Do this for a few months and you have moisture.
If the fuel tank was under a pressure you would hear it release when you removed the cap, same with a vacuum.
Now if the vehicle was parked in a garage then I feel you would have alot less of it due to the fact the temperature is more stabil.
The gasahol soaks up moisture like a sponge.
The best advice I have seen here is to use gas stabilizer. Up here in the Adirondacks, where moisture and temperature extremes are a problem, I have gas over a year old that has stabilizer in it and have not had a problem. Particularly in the boats that are on the water all summer and not used much it works to keep the gas fresh. I use it even if I think I might use up the gas soon. Also, if you can get non-ethanol gas and still use the fuel stabilizer, you should be good to go. 1 ounce of the stuff treats 2.5 gallons. 32 ounces should cost about $12.00 at discount stores.
You don’t have to start thinking about age problems until the gas gets older than 6 months or so.
If you drive it 2000 mi per yr at 15 mpg, that’s about 140 gallons, or around 12 gallons per month. So if you drive it regularly, about a half tank per month, and the gas is not sitting long enough for age to be a problem.
On the other hand, if you let it sit and drive it once every six months, then I would leave minimal fuel in it while it sits, add some fuel treatment, and then pump in more fresh gas at the start if your next trip.
I agree. It is just as important to keep the tank full if you do drive fewer miles. 2k a year is still enough to refresh your fuel several times during the summer, which is the most " active" time for fuel break down. I would add stabilizer from a marine supply store for ethanol just to be safe. I would not let the fuel level go below one half a tank…which seems like a good compromise. Be aware ! Ordinary stabilizer not made for ethanol will not work anywhere near as well. Don’t be cheap and pay more for that which is.