# Why do you top off your gas tank? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [February 5, 2011, 5:58pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296 "2011-02-05T17:58:24Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [February 5, 2011, 9:55pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/21 "2011-02-05T21:55:25Z")
I try to top it off and sometimes bounce the car a little to get more in. The motivation is that stopping for gas is a disruptive hassle, especially in nasty weather. If larger tanks were an easy option to buy, I’d buy them. Roughly, I’m estimating that each second spent pumping gas gets me an extra ten or twenty minutes of driving, so extending a gas stop that is already required by several seconds seems like a good bargain. I’ve heard about emissions systems problems from topping off, but heard they are rare and mostly occurred in just the first few versions of these systems before they learned how to make them more resistant to flooding. I’ve never had any trouble with this in my cars (unless the trouble can escape notice of the driver and the emissions testing station). Is this stupid? ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [February 5, 2011, 10:11pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/22 "2011-02-05T22:11:34Z")
> [@Superhal](#): > > The nozzle shuts off because of a vapor sensor in the tip. However, the gas dispensed is measured at the pump. Therefore, some of the gas you’ve paid for is still in the nozzle and hose. > > If you click after the pump stops you get a little bit of that overcharge. > > Don’t worry about it though, it evens out. You get that little extra from the previous user, and your extra goes to the next person. You must think that the extra click dispenses gas that the first click doesn’t. It doesn’t work that way. If you want the last few drops, wait for it to drain out, jiggle the hose, or change the angle of the nozzle. Starting the pump again won’t make the last few drops come out without charging you for it, it just sends more gas into the hose and registers it on the meter. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [February 5, 2011, 10:19pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/23 "2011-02-05T22:19:16Z")
> [@AshenLady](#): > > I ask that my tank doesn’t get topped off. If the gasoline spills, it ruins the paint. It’s much worse than that. In addition to ruining the paint outside of the tank, topping off can force gasoline into the emissions system. You can do things like force gasoline into the charcoal filter, which will ruin it. This will cause your check engine light to come on, and in some states this will prevent your car from passing inspection until you get it fixed. Those little charcoal filters aren’t cheap, either. Expect to pay a couple hundred bucks to replace it. Never top off. It’s not worth the risk. As Gary T said above, if you do, he or one of his colleagues will thank you for your business. ---
**Author:** ![flatlined](https://avatars.discourse-cdn.com/v4/letter/f/eb9ed0/32.png) [@flatlined](https://boards.straightdope.com/u/flatlined)\ **Post date:** [February 5, 2011, 10:23pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/24 "2011-02-05T22:23:11Z")
> [@aceplace57](#): > > My Dad puts his foot on the bumper and bounces the car up/down a couple times. Gets an extra pint of gas that way. 😃 > > Why ?? \ It makes him happy. My sweet baboo does this. I’ve never asked, there are some things I really don’t want to know. ---
**Author:** ![Balthisar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/balthisar/32/2825_2.png) [@Balthisar](https://boards.straightdope.com/u/Balthisar)\ **Post date:** [February 6, 2011, 5:44am UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/25 "2011-02-06T05:44:24Z")
> [@engineer\_comp\_geek](#): > > It’s much worse than that. In addition to ruining the paint outside of the tank, topping off can force gasoline into the emissions system. You can do things like force gasoline into the charcoal filter, which will ruin it. This will cause your check engine light to come on, and in some states this will prevent your car from passing inspection until you get it fixed. Those little charcoal filters aren’t cheap, either. Expect to pay a couple hundred bucks to replace it. Never top off. It’s not worth the risk. Only some cars are susceptible to this via overfilling (earlier Taurus, for example). The thing with the charcoal filters is, they’ll eventually dry back out. You really won’t ruin them. You may _think_ you’ve ruined them for a few months, but remember, gasoline evaporates. Me? I’m stoopid I guess. When the pump stops, I usually get another half-gallon. Since I average about 22 mpg, that’s another 11 miles. And since I usually wait until I’m empty, that’s often an extra day between fillups. Yes, I understand that a lot of people like to worry about contingencies, but I never leave the metro area, and I have AAA. On Edit: the truck I try to keep above half a tank. Because I don’t drive it regularly, I worry more about condensation and $80 fillups. Logically the $80 fillups don’t matter, because the cost is the cost. But if I put in $40 once per month rather than $80 once every two months, then I feel better, and that’s all that matters. ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [February 6, 2011, 6:14am UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/26 "2011-02-06T06:14:22Z")
It has been illegal for the attendant to top off the tank in Oregon for about a year and a half. > **[Topping off gas tanks now banned in Oregon](https://www.oregonlive.com/environment/2009/07/topping_off_gas_tanks_now_bann.html)** > > The Associated PressIn this 2008 file photo, gas spills out as a customer tops off her fuel tank in Lawrence, Mass. An Oregon law banning topping off tanks goes into effect today. If you ask a gas station attendant to... And of course, it is illegal for me to pump my own gas here too. ---
**Author:** ![thirdname](https://avatars.discourse-cdn.com/v4/letter/t/d07c76/32.png) [@thirdname](https://boards.straightdope.com/u/thirdname)\ **Post date:** [February 6, 2011, 7:34am UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/27 "2011-02-06T07:34:21Z")
> [@Shagnasty](#): > > Sometimes I wonder what would happen if I were in a high speed car chase with a madman and that three extra miles made the difference between life or death. Other times, I think about it as a trip to the emergency room where seconds count or running out of gas in the middle of nowhere during a blizzard. People may scoff but all it takes is one time for it to be completely worth squeezing in those last few drops of gas. If you’ve ever watched COPS you should know that car chases don’t usually last very long before someone crashes, a car breaks or some such. Personally, if someone ever follows me in my car I will just drive to my local police station. Anyway, if you’re concerned about how much gas you have, filling up more frequently will make a much bigger difference than topping off the tank. ---
**Author:** ![Harborwolf](https://avatars.discourse-cdn.com/v4/letter/h/c89c15/32.png) [@Harborwolf](https://boards.straightdope.com/u/Harborwolf)\ **Post date:** [February 6, 2011, 1:17pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/28 "2011-02-06T13:17:26Z")
Meh. I just fill to the next rounded number. Makes it easier for my poor, feeble mind to do the math on my bank account. If I have to repeatedly click, it’s because I keep going over. If it gets too toppy, I just give up. ---
**Author:** ![davidm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/davidm/32/225_2.png) [@davidm](https://boards.straightdope.com/u/davidm)\ **Post date:** [February 6, 2011, 1:40pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/29 "2011-02-06T13:40:47Z")
My owners manual specifically states that I should stop when the nozzle clicks off and not try to top off the tank. It probably wouldn’t say that without a reason. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [February 6, 2011, 1:41pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/30 "2011-02-06T13:41:27Z")
The real reason people do irrational things is because it makes them sleep better at night. In preparation for ever needing to defend their irrational position, they will create a list of reasons that make sense (to them). Irrational behavior then leads folks to ignore sound reasoning or drive the person making the rational argument crazy. At this point, the irrational person, defending their irrational behavior, looks incredibly sound, as they are faced with someone ( an otherwise rational person) that is now the insane/crazy person. This bolsters the irrational person’s position. If you have a friend, co-worker or loved one (and\*\* especially\*\* a spouse) that does silly things with their car (put it in neutral at every stop; drive backwards a block every day to even out wear; open the hood on hot days when the car is in the sun… etc) do yourself a favor and let them do it. Don’t even approach it rationally. It ain’t worth it. . ---
**Author:** ![davidm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/davidm/32/225_2.png) [@davidm](https://boards.straightdope.com/u/davidm)\ **Post date:** [February 6, 2011, 1:45pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/31 "2011-02-06T13:45:04Z")
Philster, I’d agree with you up to the point where they may be damaging the car. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [February 6, 2011, 2:40pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/32 "2011-02-06T14:40:52Z")
I doubt if many cars are built like this today, but my VW bug, which had a 10.6 gallon tank, had a very short filler neck. When the nozzle said it was full, there was a 4 gallon space left, so you betcher ass I topped it off. The same thing happens in my motorcycle. If I relied upon the automatic shutoff, I would have an empty tank, since the nozzle hits bottom when inserted fully. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [February 6, 2011, 2:53pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/33 "2011-02-06T14:53:09Z")
> [@Musicat](#): > > The same thing happens in my motorcycle. If I relied upon the automatic shutoff, I would have an empty tank, since the nozzle hits bottom when inserted fully. Yep. I have to hold the nozzle tip just at the lip inside of the lid. And in California, where vapour boots are common, I had to use both hands so that I could hold the boot up. (Otherwise it wouldn’t pump.) I had a girlfriend who had a friend who was inspired by her bike (we both had XJ600s), and he bought a motorcycle. He complained that he could only go about 50 miles on a tank. Yep, he just stuck the nozzle in and took it out when it clicked off. He was only getting a gallon of fuel. How do they do motorcycles in Oregon? Do the attendants know how to fuel them? Or do riders have to instruct them each time? ---
**Author:** ![don\_t\_ask](https://avatars.discourse-cdn.com/v4/letter/d/e68b1a/32.png) [@don\_t\_ask](https://boards.straightdope.com/u/don_t_ask)\ **Post date:** [February 6, 2011, 2:57pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/34 "2011-02-06T14:57:07Z")
Years ago I started a thread about stupid stuff people do [with this OP](http://boards.straightdope.com/sdmb/showthread.php?t=498801): **Really, head scratchingly, stupid things that people do.** Today is the cheap day to fill up your car in Sydney, so I did. The guy next to me, when the pump cut out, pulled the nozzle out a bit and drizzled in another cup of juice. I said to him, "I have to ask. Are you planning to drive on that tankful until the point that you actually need that last little bit?’ He laughed and replied, “Habit.” ---
**Author:** ![Count\_Blucher](https://avatars.discourse-cdn.com/v4/letter/c/c5a1d2/32.png) [@Count\_Blucher](https://boards.straightdope.com/u/Count_Blucher)\ **Post date:** [February 6, 2011, 3:02pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/35 "2011-02-06T15:02:11Z")
> [@Stratocaster](#): > > I want to maximize the time / distance between fill-ups. This. Every time you fill up, its X minutes of free time out of your day at the rate you’d pay yourself at work, because its Your free/off time. To minimize this expense and maximize your free time, you buy the limit of what you need. Its the same reason you’d stock up on what you need once a week or more at a grocery store: you realize in advance that you will go through (substance X) & having to make even one unplanned trip to the store during the week is against your best interest and cuts into your personal time bottom line. Companies who employ you use MBA tricks to maximize their profits. Why can’t you use these same tricks against these same companies to maximize your free time as a consumer? ---
**Author:** ![minor7flat5](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/minor7flat5/32/258_2.png) [@minor7flat5](https://boards.straightdope.com/u/minor7flat5)\ **Post date:** [February 6, 2011, 3:56pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/36 "2011-02-06T15:56:41Z")
> [@Gary\_T](#): > > A few extra miles or a slightly more precise mileage calculation (probably less than 1% difference) strike me as minimal and nebulous benefits – how often does that extra three miles of range really make a difference in how often you need to stop for gas? > > Avoiding the possibility of screwing up part of the evaporative emission control system by pushing liquid into a device designed only to deal with vapors strikes me as a worthwhile benefit (could cost hundreds to evaluate and repair). > > Do what you want, but I’d say the reasons to top up are weak and contrived. If you do mess up your EVAP system, I or one of my colleagues will thank you for the business. 🙂 I never said that the mileage argument was compelling, just that it was a valid one. It’s one of those things where we waste our time trying to perfect one small detail, while the big picture is messy enough that our efforts are in vain. I never knew that there was an expensive emission control system doodad in there. Now I know and I will refrain from topping off. It’s a moot point for me most of the time anyway—I live in Jersey, and they don’t let us pump our own gas. ---
**Author:** ![Lanzy](https://avatars.discourse-cdn.com/v4/letter/l/74df32/32.png) [@Lanzy](https://boards.straightdope.com/u/Lanzy)\ **Post date:** [February 6, 2011, 4:01pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/37 "2011-02-06T16:01:34Z")
When my wife’s Nissan stops its full, I’ll squeeze 1-3 pennies worth to round off. When my Ford 150 stops its got 2-3 gallons left to go, I’ll squeeze off another few dollars worth. And you’re right about the bikes, I don’t think I’d trust an attendant to know how to fill my Burgman. ---
**Author:** ![El\_Kabong](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/el_kabong/32/496_2.png) [@El\_Kabong](https://boards.straightdope.com/u/El_Kabong)\ **Post date:** [February 6, 2011, 4:15pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/38 "2011-02-06T16:15:56Z")
> [@Mangosteen](#): > > Instead of going 200 miles before you have to fill up again, you can now go 203 miles? > > I see people at the gas pumps all the time, click click, click click, trying to get that last ounce of gas into their tank. > > What the heck are they doing??? I always thought they were betting on the price of fuel having risen by the next time the fill up. Hey, I’m not claiming it’s rational. ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [February 6, 2011, 4:17pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/39 "2011-02-06T16:17:44Z")
> [@Shagnasty](#): > > Sometimes I wonder what would happen if I were in a high speed car chase with a madman and that three extra miles made the difference between life or death. Other times, I think about it as a trip to the emergency room where seconds count or running out of gas in the middle of nowhere during a blizzard. People may scoff but all it takes is one time for it to be completely worth squeezing in those last few drops of gas. As others have said, I used to put gas in to round it to get less pennies in change. I also used to be a pump jockey in the 70’s, so I suspect that some of it came from that. I don’t bother anymore, and very rarely let my car get below a 1/4 of a tank. I usually fill up at about 1/2 tank. The closest gas station is a good 20 miles from my house. I just like to be sure. ---
**Author:** ![Mangosteen](https://avatars.discourse-cdn.com/v4/letter/m/6a8cbe/32.png) [@Mangosteen](https://boards.straightdope.com/u/Mangosteen)\ **Post date:** [February 6, 2011, 5:13pm UTC](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296/40 "2011-02-06T17:13:33Z")
OK, I get it. If you top off, instead of having to go to the gas station 25 times a year, you only have to go 24 times. However, the extra minute you spend at the gas station topping off, means that you could has spent that extra 24 minutes of your time doing something else. [Previous page](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296.md?page=1) [Next page](https://boards.straightdope.com/t/why-do-you-top-off-your-gas-tank/570296.md?page=3)