我刚在网上查了查，看来这种观念不正确。还是应该保持油箱有油

When is it best to refill a tank of gas?


Most interested in learning what's best for the engine. Would be interesting to consider several other factors and view it as an optimization problem.



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Ryan Carlyle



Ryan Carlyle, BSChE, engineer at an oil company
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Marc Bodnick,



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I have a few important reasons outside your vehicle's mechanical behavior to keep your tank half full or better.

Whenever there is a natural disaster, disease outbreak, major holiday, or other reason for a large number of people to leave the cities at once, everyone will want to fill up at the same time in the same place. Keeping your tank on the low side most of the time increases your risk of getting stuck in gas station lines, or running out of fuel when the highways jam up, or other screw-ups that can range in severity from inconvenient to calamitous. Do not be the sucker waiting in a 6 hour gasoline line when an evacuation is ordered. Do not be the poor schmuck who runs out of gas and is stranded when a natural disaster is about to hit. Always, always, always keep enough fuel in your tank to get out of town in a hurry. This is basic emergency-preparedness.

The other reason to keep your tank at least half-full is national energy security. One of the dark secrets of the world's energy infrastructure is that it has very little centralized storage capacity -- creation of government stockpiles like the US Strategic Petroleum Reserve has actually caused the private sector to decrease their storage capacity to just barely cover minor supply shocks and seasonal demand fluctuations. World fuel and oil supply is entirely based on constant pipeline flows and tanker traffic -- if the flow is disrupted by war or disaster for even a few days, localized shortages appear almost immediately. It's actually a very robust system, and the shortfall is always made up via redistribution of existing supply, but there is a considerable delay (1-2 weeks) before supply lines can be rerouted.

So how does this affect you, the individual driver? Gasoline production is very well-balanced with average demand, and enough fuel is always made to supply everyone. The real problem isn't lack of fuel, it's too many people trying to fill up at once. If the media whispers the word "shortage," everyone rushes out to fill their tank at once. You can't top off all the cars in the country in a day. All the gas stations and distribution depots in the country have considerably less total storage volume than everyone's individual vehicle tanks added together. So there doesn't have to be a real supply shortage! Just the threat of a shortage causes people to overwhelm the system, creating an artificial shortage for a week or so until the oil and fuel flows can catch up.

By keeping your tank over half full, you can ride out both real supply shortages (which clear out in a week or two) and panic-induced fake supply shortages (which also clear out in a week or two). Do not be part of the panic. Do not contribute to the world's susceptibility to energy supply disruption. Do your part to improve your country's national energy security by using your vehicle as rolling fuel storage. If everyone always kept their tanks over half full, it would double the world's normal fuel storage levels.







Written 16 Feb, 2013.




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Jeremy Karmel, Quora User, (more)





Advice #1 Don't let the the gasoline level get very low, as in under 1/10 of a tank or under 2 gallons. Don't run the tank dry.

That low fuel level will cause the fuel pump to suck up all the crap & water in the very bottom on the tank, causing a shorter life for the fuel pump ( $400 replacement cost).

That crap will can also clog the Fuel filter, robbing the engine of power, or possibly stopping the engine. (fuel filter change, $35-85 range)

If the crap get to the engine (the filter should stop it), and it is a fuel injection type, that's really bad.

If the car will sit for a long time - airport parking lot? - try to have the tank close to full to reduce condensation from temperature cycling. The newer sealed fuel systems have reduced the effect of temperature cycling, so this advice may not be as important as it once was. If your car is more than say 4-8 years old, there could be a seal failure however, and having an almost full tank would reduce condensation.

Advice #2 You also should try to buy gasoline each month, because of the anti-gumming additives and the seasonal adjustments to gasoline composition.

If you have summer time gasoline from June in your car on a cold December day, it maybe much harder to start, because the June gas has low vapor pressure. Add in a weak battery, and you might fail to start.
If you have January winter gasoline in your car, and fuel system is well sealed, there will be a lot of high vapor pressure parts in the gasoline, like butane (which you can sometimes smell in winter gasoline). This can be a problem in the summer. Your car should start fine - the first time, when it is cold. But, if it is a real hot day, you might "vapor lock" stopping the engine while driving.(worst case). Most likely, if you park the car, come back in a few minutes, and try to start, the heat soak from the engine being stopped after running will heat up the fuel lines, causing vapor lock. Result - your car won't start for about an hour until everything cools way down.







Updated 4 Nov, 2012.




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Andrew Hennigan



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Ian C. Ward, Quora User, (more)





One other tip a friendly owner taught me one day is that you should avoid filling up when you can see a delivery in progress or just completed. Pumping new fuel into the tanks stirs up the water and crud so you are more likely to pick up some contamination.







Written 16 Feb, 2013.




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Ian C. Ward



Ian C. Ward, former Systems Engineer at Top... (more)
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James Ide, Quora User,



Ryan Carlyle, (more)





In addition to Bill's recommendations (which are related to gasoline's interaction with the mechanics of your car), I would pose the following recommendations (which are related to the physics and nature of gasoline):

#1: Fill up at half tank for fuel efficiency
This is related to a lot of factors, including gasoline's tendency to evaporate at temperatures not much higher than room temperature, which reduces the pressure on the fuel line.
If you'd like to test this, next time you fill your tank all the way up, reset your trip-odometer. Drive the car until half tank, and fill it back up again, recording how much you put into your tank and your trip-odometer reading. Divide the miles driven (your trip-odometer) by the amount you put in your tank to get your MPG. Then, reset your trip-odometer and drive until your vehicle's "Low Gas" light comes on, and repeat the earlier steps of computing your MPG. Half tank will consistently give you better numbers.

#2: Fill up when it's cold outside
This won't prove as dramatic as #1, but it helps a little bit. Gasoline expands when it heats up, providing less available energy per unit of volume. Gasoline filling stations in the US are not required to compensate for temperature variations when selling product to end consumers. However, Canada does. So another recommendation would be to move to Canada.

#3 Don't worry about preferring one brand of gasoline over another
Different brands of gasoline don't make as much of a difference as the Gas company's marketing wings would make you want to believe. The additives are the only thing that make much of a difference, and just how most people can't tell the difference between Pepsi and Coke, your car won't notice much of a difference. The US Government mandates minimum requirements for gasoline additives, and you'd be surprised that a lot of what you find at the pump has nothing but a generic additive (even for branded gasoline locations). For example, up until about 2-3 years ago, pretty much all gasoline sold in the Central Florida area had nothing but the generic additive in it. Except that ExxonMobil is special. Their gasoline had 2x the generic additive as everyone else (it's amazing how true this stuff actually is...).







Updated 9 Nov, 2012.




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Danny MaioraniDanny Maiorani, German Auto Shop Owner, former... (more)
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You should fill up whenever you feel like it, as long as you don't run the vehicle often with less than a couple gallons in the tank.

The statements about running low and siphoning crap off the bottom of the tank aren't really applicable to modern day cars. Modern vehicles have the fuel pumps submerged in a small bucket or swirl pot in the fuel tank. Additionally, the pump will normally have a mesh screen attached to it in the tank. Unless the vehicle has returnless injection, the vehicle constantly pumps fuel from the tank to the engine, and what isn't used is then returned to the tank.

This can cause tank temperatures to reach a couple hundred degrees in extremely hot weather, and heat is the enemy of electric motors. The fuel pump is technically fuel cooled, so the more fuel, the cooler the pump stays, and the longer its life.

So if your question relates to fuel pump longevity, the answer is to keep as much fuel as possible in the tank, because it extends fuel pump life, and keeps moisture out of the tank.

However, you could also argue that hauling around all that extra weight costs more money in lost efficiency, thereby negating the savings in not ruining the pump, and depending on your mechanical ability and the cost of a pump on your vehicle, it could be cheaper over the life of the vehicle to run it as low as possible. It's not a dumb question, but to get a straight answer requires clarification of your intent really.