# Why top off when filling gasoline? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [April 28, 2018, 3:35pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267 "2018-04-28T15:35:39Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![QuickSilver](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quicksilver/32/7832_2.png) [@QuickSilver](https://boards.straightdope.com/u/QuickSilver)\ **Post date:** [April 29, 2018, 4:09pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/41 "2018-04-29T16:09:20Z")
> [@k9bfriender](#): > > I’ve had a few times when the pump stopped well short for some random reason, and still had plenty to go, but for actual top off situations, it’s not 2 gallons that are getting in there, more like 2 ounces or so. > > If you have an odd tank, that may change things, but I don’t think that’s the case for the vast majority of vehicles out there. > Anyway, both of you have said that you can put 2 gallons in after the pump cuts out. Is this common? Every car I’ve ever had or filled you could only cram a little bit more into. I don’t know if it’s common. It is/was common in my VW’s and Volvos. My MB really means it, so I can only top it up to the nearest dollar. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [April 29, 2018, 5:34pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/42 "2018-04-29T17:34:22Z")
> [@DesertDog](#): > > So, basically you were stealing those few ounces from the next customer, who’s expecting the sale to start with the usual already-filled hose. When I was young I had a friend who did that – shutting off the pump, opening the valve, then walking the high point of the hose towards the nozzle to let it drain into his tank. He had the decency to look embarrassed when I cocked an eyebrow at him. I do wonder if I’m ripping off the next person when I do that, but it’s not much gas, I’m not doing as you said and pushing the siphon along. I mostly do it to avoid dripping gas down the side of my car when I pull out the nozzle. ---
**Author:** ![Corry\_El](https://avatars.discourse-cdn.com/v4/letter/c/ecae2f/32.png) [@Corry\_El](https://boards.straightdope.com/u/Corry_El)\ **Post date:** [April 29, 2018, 5:40pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/43 "2018-04-29T17:40:55Z")
> [@Flyer](#): > > You forgot to qualify that statement with “except for the sensible people.” > > You see, sensible people understand that basic precautions should be taken against card fraud, skimmers, etc. Even apart from that, we understand that sometimes the card readers have trouble, or the satellites go down, etc. To not carry cash is incredibly stupid and ignorant. > > We also understand that to pay interest on ordinary purchases is also incredibly stupid. Most people who have credit cards carry a balance, and the more that people use their cards, the higher the balance is likely to be. > [https://www.creditcards.com/credit-card-news/credit-card-debt-statistics-1276.php](https://www.creditcards.com/credit-card-news/credit-card-debt-statistics-1276.php) Sorry to pile on but that’s pretty ridiculous as stated. I haven’t paid cash for gasoline in decades and have never in that time been left entirely high and dry due to problems with both credit cards I carry plus my debit card, or the pumps. And even then I do have cash on me, but I still wouldn’t go through the definitely non-sensible ritual of topping off. I’d just get change that one time every many years nothing but cash would work at a gas station. Nor have I paid interest on a credit card balance, ever, using credit cards as much as possible for the cash back and the float. The only rational reason to use cash at gas stations is if there’s a price for cash lower than credit price by more than cashback. With the main card I used for gas giving 5% cashback that’s never been true where I get gas. Or I guess exceptional cases where a person can justify the privacy advantage (in terms of someone tracking the card) in a non-paranoid way. The reference to the link is the classic fallacy of using average statistics for something where you can make the personal choice not to be like the average. Nobody puts a gun to anybody’s head to run a credit card balance, and I never ever do. ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [April 29, 2018, 6:17pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/44 "2018-04-29T18:17:28Z")
I would think one good reason for topping off is so that you can make an accurate mileage calculation. I let mine run until the first click off for that same reason. Some cars don’t click off in the same place every time. ---
**Author:** ![ekedolphin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ekedolphin/32/10003_2.png) [@ekedolphin](https://boards.straightdope.com/u/ekedolphin)\ **Post date:** [April 29, 2018, 10:46pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/45 "2018-04-29T22:46:00Z")
I don’t top off, and I mostly use cash for gasoline. I put $40 in the stash can every time one of us gets paid. Shell gives me three cents off per gallon for cash. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [April 29, 2018, 11:21pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/46 "2018-04-29T23:21:56Z")
I did try topping off once with my new Forester, and got 1.25% more gasoline into the tank. It hardly gives an improvement in the frequency of stopping to fill up, and might damage the emissions control system (or so they say, but I’ve read that actually means saturating a carbon filter, and in my car that filter is up in one of the rear roof pillars above the fuel receptacle so I don’t think that could happen). ---
**Author:** ![california\_jobcase](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@california\_jobcase](https://boards.straightdope.com/u/california_jobcase)\ **Post date:** [April 30, 2018, 12:37am UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/47 "2018-04-30T00:37:18Z")
I have had a couple of cars that simply wouldn’t let me fill the tank (approach manufacturer-stated capacity) without going through filling, shaking the car and jostling the bumper, and then pumping in the last two gallons. The worst offender was a 1983 Datsun Nissan Sentra Diesel, so those two gallons meant an extra 100 miles range when I was on the highway. The reasons this car acted this way was a combination of diesel fuel foaming and a sharp curve in the fuel filler neck. The car had no emission control stuff since diesels were exempt back then. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [April 30, 2018, 4:01am UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/48 "2018-04-30T04:01:13Z")
When I do top off, it feels like a reflexive holdover from the Carter administration, putting as much gas into the tank as I could get because I didn’t know for sure when I’d be allowed to buy gas again. ---
**Author:** ![BeeGee](https://avatars.discourse-cdn.com/v4/letter/b/b5a626/32.png) [@BeeGee](https://boards.straightdope.com/u/BeeGee)\ **Post date:** [April 30, 2018, 4:18am UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/49 "2018-04-30T04:18:38Z")
This sensible person has two credit cards that are only used for gasoline purchases. I get a discount per gallon for using them. I drive a Corolla so a tank of gas lasts me a long time. I get an email every time the card is used and i pay off the balance every month. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [April 30, 2018, 11:18am UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/50 "2018-04-30T11:18:12Z")
I will let go to the first clickoff, then give it one more, sometimes that first one is premature. Though sometimes I can hear the fill up, the tone changes of the fluid flowing in the tank, if that is heard then I’ll let it just click off the first time. Beyond that rarely, however… I had a car with something like a 16 gal tank, if I could go slowly at the end I was able to get 19 gallons in it, probably it had a non-CEL damaged vapor return system and a destroyed charcoal canister. I didn’t have to click, click, click it, but just go slow. Those extra gallons meant I only had to fill up every 3rd day of driving for work, instead of 2 days and it was nice to just go straight home, and stopping in the morning was an equally unpleasant option. I do have to say that those clickers/thumpers are somewhat annoying when that pressure pulse is also felt in the pump one is using. ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [April 30, 2018, 12:02pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/51 "2018-04-30T12:02:53Z")
> [@california\_jobcase](#): > > I have had a couple of cars that simply wouldn’t let me fill the tank (approach manufacturer-stated capacity) without going through filling, shaking the car and jostling the bumper, and then pumping in the last two gallons. I have seen some unfortunates go through that ritual but not in a couple years. It would be understandable and obvious from watching that they’re not squeezing in a half-gill so they can get their credit charge to be a magical $25.00 flat or maybe brag, “I got 32.48264 miles per gallon!” instead of a mere 32.47863, forgetting that no matter what their calculator tells them their accuracy is only three or four significant figures anyway. ---
**Author:** ![PoppaSan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/poppasan/32/189_2.png) [@PoppaSan](https://boards.straightdope.com/u/PoppaSan)\ **Post date:** [April 30, 2018, 12:15pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/52 "2018-04-30T12:15:32Z")
> [@ekedolphin](#): > > I don’t top off, and I mostly use cash for gasoline. I put $40 in the stash can every time one of us gets paid. Shell gives me three cents off per gallon for cash. I swipe their fuel rewards for a nickel/gallon off the top. On Tuesdays this past winter it was bumped to a dime per. Then I pay with scrip purchased from school which gives the school 5-10% cash back depending on current incentive. My school applies that to my kids’ school fees account, such as field trips, book fees, tuition. I know of one extended family that had several kids’ fees paid by one family member who was an independent cross country trucker. He did all his trips via the scrip cards. as far as topping off, my truck will kick out 3 seconds into the fill if the nozzle is on high. It only fills on medium. Over 1/2 - 3/4 gallon fits after the pump stops the first time. My Saturn not so much. It stops when it is all the way full. ---
**Author:** ![Clothahump](https://avatars.discourse-cdn.com/v4/letter/c/51bf81/32.png) [@Clothahump](https://boards.straightdope.com/u/Clothahump)\ **Post date:** [April 30, 2018, 6:27pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/53 "2018-04-30T18:27:52Z")
> [@markn\_1](#): > > Maybe I’m missing something obvious, but it seems to me you get to choose to satisfy one of these desires, not both. If you fill to a round dollar amount, the tank is unlikely to be completely full, and vice versa. Nope. I fill until the shut-off. I then keep pumping. I can usually get nearly a full gallon more into the tank, but I will stop pumping on a round number. Is it absolutely 100% full? Well, it’s not overflowing the fill pipe, but it’s more gas than the pump thought I should have, so…close enough for me. ---
**Author:** ![control-z](https://avatars.discourse-cdn.com/v4/letter/c/eada6e/32.png) [@control-z](https://boards.straightdope.com/u/control-z)\ **Post date:** [April 30, 2018, 7:57pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/54 "2018-04-30T19:57:01Z")
I think it’s a little OCD, I like to top off to the nearest 10 cents, or at least 5. If I pumped $10.71 I’d go up to $10.75. Don’t judge me, and 4 cents worth of gas isn’t going to hurt anything. I guess it’s partly a game to see if I can get the pump to stop right on a multiple of 5 or 10 cents. ---
**Author:** ![JRDelirious](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jrdelirious/32/9531_2.png) [@JRDelirious](https://boards.straightdope.com/u/JRDelirious)\ **Post date:** [April 30, 2018, 8:45pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/55 "2018-04-30T20:45:50Z")
I try to take it to the next dime or quarter fraction if paying in cash just for the sake of easier change-making. If using the credit card I sometimes stop at the first shutoff, others I take it to the second, depending in the day’s mood — I do stop at the first shutoff when getting ready to return a rental car, as why give them back more fuel than they gave me. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [April 30, 2018, 8:46pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/56 "2018-04-30T20:46:22Z")
Odd how many people here still top off even tho the manufacturers and the experts say not too. 😕☹ ---
**Author:** ![Procrustus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/procrustus/32/2994_2.png) [@Procrustus](https://boards.straightdope.com/u/Procrustus)\ **Post date:** [April 30, 2018, 8:55pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/57 "2018-04-30T20:55:46Z")
> [@DrDeth](#): > > Odd how many people here still top off even tho the manufacturers and the experts say not too. 😕☹ I’m not sure we have a working definition of “top off.” Some people are adding a gallon or so, clearly more than a top off. Some people are adding $0.04 worth, probably less than a top off. ---
**Author:** ![Kent\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kent_clark/32/105_2.png) [@Kent\_Clark](https://boards.straightdope.com/u/Kent_Clark)\ **Post date:** [April 30, 2018, 9:24pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/58 "2018-04-30T21:24:30Z")
> [@DrDeth](#): > > Odd how many people here still top off even tho the manufacturers and the experts say not too. 😕☹ Not really 😕 for me. I happen to know deep in my heart that if I can’t get either the gallon total or the dollar total to end up at a nice, round exact number, life as we know it will cease to exist.:eek: ---
**Author:** ![Seanette](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/seanette/32/9139_2.png) [@Seanette](https://boards.straightdope.com/u/Seanette)\ **Post date:** [May 1, 2018, 2:40am UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/59 "2018-05-01T02:40:01Z")
> [@TCMF-2L](#): > > I calculate the MPG for the previous tankful as well as overall. > > By trying to brim the tank I am trying to fill to the same amount each time. Otherwise I would be filing to a different amount each time which would corrupt the accuracy. > > Consider this. My tank is supposed to hold about 10 (UK) gallons. Since I heed the warning from the pessimistic red low fuel lights, I rarely put in more than 8 gallons. While filling it will usually take another 1 or even 2 whole gallons after the pump first cuts out. > > A variation of 2 gallons in an 8 gallon load would make my figures out by 25%. Or that’s what I tell myself. > > TCMF-2L You sound like my husband. He does this to an even more OCD extent than you’re describing. He still has Excel spreadsheets analyzing fuel data for cars we haven’t had in years. ---
**Author:** ![Corry\_El](https://avatars.discourse-cdn.com/v4/letter/c/ecae2f/32.png) [@Corry\_El](https://boards.straightdope.com/u/Corry_El)\ **Post date:** [May 1, 2018, 1:51pm UTC](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267/60 "2018-05-01T13:51:48Z")
> [@Seanette](#): > > You sound like my husband. He does this to an even more OCD extent than you’re describing. He still has Excel spreadsheets analyzing fuel data for cars we haven’t had in years. I have it in one spreadsheet, but yeah every fill up for cars I don’t even have anymore. 🙂 However I still don’t buy TCMF-2L’s logic about topping up wrt to tracking mileage. Filling the tank to the same exact level each time would be a necessarily condition for the calculated mileage on each tank to be exactly comparable. But it wouldn’t be a sufficient condition since the driving conditions also vary on each tank (what % ‘city’ or ‘highway’ often does, or even if all ‘highway’ the temperature, how hilly, delays for construction etc). Whereas the overall calculated mpg under your overall driving conditions is as accurate as the odometer and gas station pumps are over a series of tanks without any topping up. The small variations from tank to tank due to the pump clicking off at slightly different amounts averages out to zero in the long run. I also highly doubt 2 gallon differences if there’s nothing wrong with car or pump. [Previous page](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267.md?page=2) [Next page](https://boards.straightdope.com/t/why-top-off-when-filling-gasoline/813267.md?page=4)