How full to keep the gas tank?

Question:

If the car runs, there is fuel in the pump, it’ll stay cool enough. Many cars have pumps outside the tank – they don’t overheat. When you think you need gas because you might run out, get some. EFI cleaners (A good one, not CRC or Wynns or some other cheap gas-in-a-can) are good to run through periodically – they help soften any deposits which can build up, but the main thing is they emulsify with water in the tank so it can be burnt in the engine.Water in the system is bad Allan

– Hide quoted text — Show quoted text -> ||….never let the gas tank get almost empty. > ||….always fill up before the tank is 1/4 full. > Almost all modern cars have a fuel pump immersed in the fuel tank, with the > motor above the pickup point. When it gets low, the motor can be partially > uncovered.  Since the motor is cooled by the fuel running through it and around > it, it can run hotter if the fuel level is very low.  Habitually running the > tank to the last drop can shorten the life of the pump. > OK. I hardly ever drive the car to the point where the GAS light comes on, > and if it comes on when I am driving, I fill up. > Do you think that I am safe, or should I fill up when the tank is 1/4 full? > — > http://www.bushflash.com/thanks.html > "Bubba got a blowjob, BU$H screwed us all!" – Slim > http://www.worldmessenger.20m.com/weapons.html#wms > George "The AWOL President" Bush: http://www.awolbush.com/ > WHY IRAQ?: http://www.angelfire.com/creep/gwbush/remindus.html > http://www.toostupidtobepresident.com/shockwave/chickenhawks.htm > VOTE HIM OUT! November 4, 2004

Response:

Whats more, many of the pumps are located at the top of the tank, and the pickup sits underneath it. The pump could be uncovered at only half a tank Look at a nissan skyline Allan

– Hide quoted text — Show quoted text -> ||> Habitually running the > ||> tank to the last drop can shorten the life of the pump. > || > ||I’m not buying it. Have any citations that discuss the motor-pump assembly > ||operation? > Here’s a start. A google search gets lots of hits. > http://www.alldata.com/techtips/2002/20020920d.html > Thanks. This site seems to focus on running a fuel pump without fuel, which I > agree is "not good" for the pump. I’m more curious about your claim that the > pump’s motor is not adequately cooled when the fuel tank falls below, say, 1/4 > tank. > I did google and saw several sites claiming pretty much as you do on this. And I > found just one internet forum site where someone argued along the lines I do, > with his own experience to back it up. > http://www.canadiandriver.com/discuss/messages/68/14277.html?1087480360 (see > Articsteve’s comment). > I have a 1991 Civic (fuel injected) and it has a fuel pump in the fuel tank. I > bought the car new and have almost always run the car until it was down to 15% > or more of the fuel tank’s capacity, filling the 11.– tank with at least 10 > gallons most of the time at fill-ups. No problems that I’m seeing. The car has > 153k+ miles on it. > Also, your explanation doesn’t make sense to me, as cooling flow around the > motor comes, you seem to claim, from the pump itself. The pump will move fluid > as long as its inlet is submerged. Plus, even if the motor becomes uncovered at, > say, 1/4 tank, I’m not buying that the relatively stagnant surrounding air can’t > adequately remove its heat. It can’t be a very high horsepower motor, after all. > (Some electric pumps are located outside the fuel tank, so submersion isn’t at > all needed for cooling of them. Are these pumps’ lives shorter? Not that I’ve > ever read.) I’m not even sure that the assembly becomes uncovered until very low > fuel levels–much lower than 1/4 tank, I bet. Otherwise, it seems like the > owner’s manuals or various service manuals would warn about this. Mine does not, > for one. Nor does Chilton’s. > But again, I see all the sites that make the claim you do. I certainly don’t > want to argue with folks who want to err on the safe side, especially since > there are other good reasons not to drive until nearly empty.

Response:

I got 180,000km on my 1998 Civic Hatch. I normally fill up when there’s only 7% to 15% left in the tank. In several occasions, I’ve filled 44 litre (the tank can take 45 litre capacity). In the summer, when the weather is hot, I usually try not to go under 7%. Pars – Hide quoted text — Show quoted text – > snip > Here’s another: > http://pages.sbcglobal.net/gorf/bmwtips/maintfuelpump.html > Now I’m totally paranoid about ever again driving my car with less than "a few > gallons of gasoline" in it.  ;-) > After 13 years and 153k miles on the 1991 Civic, with no fuel pump problems, I > reckon I’ll just keep risking it. I’ve always wanted to have to replace a fuel > pump, anyway. > (Seriously: I agree with Rex that folks should err on the side of what they feel > is safest for their auto-mobiles. Plus, hey, a few gallons in Honda’s biggest > car is pretty low on gas. It’s still over about 20% on my car.)

Response:

> Ha ha… I know what you mean. > Of course Honda’s distributor design is flawless.

eh- better than some, worse than others. thanks to the internet, we can share problems and solutions like this. id rather have a common, fixable problem than an uncommon, hard to fix one.

Response:

- Hide quoted text — Show quoted text – >|| >||I do like y_p_w’s theory about a full tank tending to prevent condensation >etc. >||buildup. I’ve seen this discussed before. E.g. from the Car Talk guys re >winter >||driving: >|| >||http://www.cartalk.com/content/features/WinterDriving/ >|| >||The other reason for a full tank is that warm daytime temperatures will fill >the >||empty space in the tank with moisture, which will condense during the cold >||night. This water will sink to the bottom and, sooner or later, rust out your >||tank. >||— >This is written about boats, which should have more problem with condensation >than cars.  Boats do not have sealed systems to the extent that cars do. >The Myth of Condensation in Fuel Tanks >by David Pascoe > Frequently we hear it said that the cause of water in fuel tanks is due to >condensation. I have long doubted this assertion but the issue has come up so >frequently that I was finally motivated to try prove to the point. The basis of >my belief or assumption is that: >There isn’t enough air volume within a tank to hold much vapor. >On average, tanks are half full, further reducing volume >The amount of water vapor in air is very small, even at 100% humidity >Conditions aren’t right to cause condensation in a fuel tank >Research produced the following values for the maximum amount of liquid water in >air at the following temperatures: >30C/86F 30 grams/cubic meter >20C/50F 17 grams/cubic meter >10C/13F 9 grams/cubic meter >There are 28 grams per ounce, so 30 grams = 1.07 oz; 17 grams = 0.6428 oz. >A cubic meter equals 264 gallons of liquid volume, therefore: >A 200 gallon tank = 0.76 cubic meter. >At 86F, an empty 200 gallon tank could contain 22.8 grams of water vapor, or >0.81 oz. >At 50F, an empty 200 gallon tank could contain 12.92 grams of water vapor, or >0.46 oz. >Note that this is the maximum amount of water vapor that a completely empty tank >could contain, in neither case a full ounce of water. >In order to condense water out of the atmosphere a surface must be much colder >than the air. The problem for the condensation in tank theory is; how do we end >up with a fuel tank that is much colder than the air? One way would be to have a >very cold day that suddenly warms up dramatically, but when does this ever >happen? The weather can turn cold very fast, but does not suddenly get very >warm. >Aluminum is second only to copper for rapid heat transfer properties; it will >therefore adjust to atmospheric temperature changes quickly. Gasoline and diesel >fuel, like water absorb [sic] heat and cold slowly. Thus one might expect to see >sweating on the outside of a tank as the day warms up from cold mornings, but do >we? Well, I can say that after 35 years of inspecting boats, I’ve rarely seen >tanks sweating. Note: Sweating may be likely to occur with boats in very cold >waters when warm days are encountered. >This issue first came up a number of years ago over a question of whether >internal engine rusting could be due to condensation caused by sudden >temperature changes as from day to night and vice versa. Since that time, >inspection of hundreds of engines showed that rust only occurs on the underside >of valve covers due to water contamination of the oil. Very few engines have >rusty undersides of valve covers, thereby proving the point that ice cold engine >blocks in the morning don

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