# Gas pumps slowing down when you get close to the purchase price.... **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [December 30, 2014, 5:05pm UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547 "2014-12-30T17:05:52Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![YogSothoth](https://avatars.discourse-cdn.com/v4/letter/y/8edcca/32.png) [@YogSothoth](https://boards.straightdope.com/u/YogSothoth)\ **Post date:** [December 30, 2014, 5:05pm UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/1 "2014-12-30T17:05:52Z")
I’ve noticed this for a while but its just hit me to post about it. When you prepay for gas, let’s say $20, then go out to pump, the pump will pump at full speed until about 20 cents before you reach your limit. Why?? We can put a man on the moon but apparently the gas pumps are too stupid to stop exactly at the purchase price? I can understand maybe 2 cents before or 5 cents before, but its consistently at like 20-25 cents before you reach the limit. Who designed this shit?? And don’t give me any guff about the station not wanting to overpump. Slowing the pump down at 5 cents does the exact same thing as slowing it down at 20 cents, plus it gets your customers out faster so more can come in during a busy period. Or just stop it exactly at the purchase price, I’m sure it doesn’t take a rocket scientist to design that ---
**Author:** ![notfrommensa](https://avatars.discourse-cdn.com/v4/letter/n/f14d63/32.png) [@notfrommensa](https://boards.straightdope.com/u/notfrommensa)\ **Post date:** [December 30, 2014, 5:11pm UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/2 "2014-12-30T17:11:45Z")
I don’t think I have paid cash for gasoline in 20 years. Heck, the only time I go in a gas station is to buy a lotto ticket. When the jackpot is high enough (pot odds) ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [December 30, 2014, 5:18pm UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/3 "2014-12-30T17:18:15Z")
The cynic in me says the gas station hopes you get bored and don’t bother to pumup the last 8 cents worth of gas. = Extra profit for the station. ---
**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:** [December 30, 2014, 5:22pm UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/4 "2014-12-30T17:22:25Z")
If you guess too close to the exact amount you need to buy, the gas can fill the fill pipe all the way to the top. Problem is, if you’re still pumping, there’s a lot of froth at the top of the gas that can confuse the sensor and cause it to stop. Once the froth dies down, you can top it up to fill the pipe and get your last $0.02 worth of gas. These are extra steps the gas vendors are not making you do. ---
**Author:** ![picunurse](https://avatars.discourse-cdn.com/v4/letter/p/7bcc69/32.png) [@picunurse](https://boards.straightdope.com/u/picunurse)\ **Post date:** [December 30, 2014, 5:29pm UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/5 "2014-12-30T17:29:43Z")
You are obviously, a child of the “Faster,Faster,Faster” generation. Does the 3 seconds it takes to finish filling when the pump slows down really affect your life or your schedule? If you let something as simple as a gas pump annoy you, you must be something of a type “A” personality. I don’t know who said it, (Maybe Ellen) but : “Don’t sweat the petty stuff, and don’t pet the sweaty stuff.” and you be a lot better off. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 30, 2014, 6:01pm UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/6 "2014-12-30T18:01:17Z")
Waay back in the computer dark ages when these were first designed, the computer in question was slower than the one in your wristwatch. And it has to monitor all the pumps. Which in a big station might be 30. So they slowed down the final bit of delivery enough to ensure they never, and I mean NEVER, gave anyone an extra penny’s worth because the computer was too slow to cycle back to your pump in time to hit the shutoff. ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [December 30, 2014, 6:08pm UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/7 "2014-12-30T18:08:41Z")
Pumping gas is a mechanical process. The electronics may know to pump $20. But theres still a mechanical pump dispensing that gas. All kinds of variables can make it go beyond $20 by a few cents. So they it slow down to accurately measure whats pumped in the last minute or so. I’m glad it slows down… I’d be more pissed if it ran over and required me to walk back into the station to pay an extra dime or quarter. That would be a PITA. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [December 30, 2014, 6:13pm UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/8 "2014-12-30T18:13:49Z")
> [@Ethilrist](#): > > If you guess too close to the exact amount you need to buy, the gas can fill the fill pipe all the way to the top. Problem is, if you’re still pumping, there’s a lot of froth at the top of the gas that can confuse the sensor and cause it to stop. Once the froth dies down, you can top it up to fill the pipe and get your last $0.02 worth of gas. These are extra steps the gas vendors are not making you do. If this is their reasoning it seems faulty. It seems to me there are mostly two types of gas purchasers: those who want $x and those who want to fill the tank. If I want it fill, it might as well treat me as someone who uses a credit card and pump fast then shut off. (If I then which to top off, I can do so. Topping is faster than their slowing process I’m pretty sure.) If I want $x, their solution only benefits me in the way you describe if I guess very closely to exactly what my tank will hold. If I have more space, just pump fast the whole way. If I guess high, just pump fast the whole way as I’ll need to go back inside for change in any case. What fraction of people are benefited by their “solution”? If your 0.2 guess is right, then assuming most people hand the cashier a bill, then only those whose tank will take between (x-1).98 and $x.00 are helped. That should be about 2% of those people who want to pay cash. The other 98% of cash payers are inconvenienced. You can change the numbers, but since the slowing starts about 20 cents before the end, it’s hard to see how more than 20% of the cash payers are helped at the inconvenience of the other 80%. If I’m trying to fill and I guess too low, the pump might as well dispense the gas fast all the way. If I guess ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [December 30, 2014, 6:36pm UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/9 "2014-12-30T18:36:18Z")
Every state has an agency that checks weights and measures. Any business caught shorting a customer faces fines and possibly criminal charges. When someone buys $20 in gas. That’s what should be dispensed. I’m not sure what the tolerance is for gas stations. Maybe two or three ounces? 4 oz is a half cup off. That’s not a lot if they are dispensing 10 gals. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [December 30, 2014, 8:57pm UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/10 "2014-12-30T20:57:56Z")
> [@LSLGuy](#): > > Waay back in the computer dark ages when these were first designed, the computer in question was slower than the one in your wristwatch. And it has to monitor all the pumps. Which in a big station might be 30. So they slowed down the final bit of delivery enough to ensure they never, and I mean NEVER, gave anyone an extra penny’s worth because the computer was too slow to cycle back to your pump in time to hit the shutoff. Is this a whoosh? I would think that the only centralized computer involved, would be the one that ties all the pumps in to the cash register. And I would think that the actual pumping action is controlled my a separate microprocessor in each pump. I’m not claiming to know any of the fact, but I just suspect that this is :dubious: ---
**Author:** ![Kimballkid](https://avatars.discourse-cdn.com/v4/letter/k/b5a626/32.png) [@Kimballkid](https://boards.straightdope.com/u/Kimballkid)\ **Post date:** [December 30, 2014, 9:37pm UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/11 "2014-12-30T21:37:01Z")
> [@YogSosoth](#): > > We can put a man on the moon Apparently we can’t even do that [anymore](http://www.space.com/7015-40-years-moon-landing-hard.html). (You knew someone had to do it. 😃 ) ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [December 30, 2014, 9:48pm UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/12 "2014-12-30T21:48:46Z")
I challenge the OP to go pour a glass or milk. Get it exactly level at the top of the glass. Did you slow down as you neared the edge? Why? I think you now have your answer for gas pumps too. Even machines are more precise when dispensing a gallon a minute instead of ten gallons per minute. ---
**Author:** ![Kenm](https://avatars.discourse-cdn.com/v4/letter/k/bc79bd/32.png) [@Kenm](https://boards.straightdope.com/u/Kenm)\ **Post date:** [December 31, 2014, 1:46am UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/13 "2014-12-31T01:46:23Z")
> [@picunurse](#): > > You are obviously, a child of the “Faster,Faster,Faster” generation. Does the 3 seconds it takes to finish filling when the pump slows down really affect your life or your schedule? It does when it’s 30 below, either temperature scale, with a strong wind. Or even in summer with the wind making the rain horizontal, so the roof over the pump area is meaningless. Anyway, it’s more like 30 seconds, not three. It doesn’t happen only with cash payments. The pumps slow to a crawl with debit-card purchases and the max price punched in. ---
**Author:** ![TBG](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@TBG](https://boards.straightdope.com/u/TBG)\ **Post date:** [January 1, 2015, 1:50am UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/14 "2015-01-01T01:50:22Z")
> [@Kenm](#): > > It does when it’s 30 below, either temperature scale, with a strong wind. Or even in summer with the wind making the rain horizontal, so the roof over the pump area is meaningless. Anyway, it’s more like 30 seconds, not three. So dress appropriately for the weather before getting out to pump, maybe? ---
**Author:** ![Kenm](https://avatars.discourse-cdn.com/v4/letter/k/bc79bd/32.png) [@Kenm](https://boards.straightdope.com/u/Kenm)\ **Post date:** [January 1, 2015, 2:59am UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/15 "2015-01-01T02:59:50Z")
> [@TBG](#): > > So dress appropriately for the weather before getting out to pump, maybe? What, and look like a wimp, eh? But the pumps are easy to confound. F’rinstance, for $20 worth, punch in $21 (a near-to-me Shell station allows cents, so $20.30) and stop the pump at $20. ---
**Author:** ![kopek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kopek/32/337_2.png) [@kopek](https://boards.straightdope.com/u/kopek)\ **Post date:** [January 1, 2015, 3:38am UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/16 "2015-01-01T03:38:24Z")
As it was explained to me, if the pump shuts off suddenly mechanically (and how else can a pump shut itself off?) at the pump side it can cause a small backwash and possible spill. That shutting it off from the nozzle side via your hand or the “you’re full you idiot” feature is just safer. Don’t know if its true – but there it is. ---
**Author:** ![Kenm](https://avatars.discourse-cdn.com/v4/letter/k/bc79bd/32.png) [@Kenm](https://boards.straightdope.com/u/Kenm)\ **Post date:** [January 1, 2015, 8:12am UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/17 "2015-01-01T08:12:53Z")
> [@kopek](#): > > Don’t know if its true – but there it is. Not true. Pumps shut off suddenly all the time when vehicles’ gas tanks, or even gas cans, are nearly full. They’re built to do so, to prevent over-filling and spills. Back pressure on the nozzle, I presume. My parents’ '51 Chevy had a whistle in the gas-tank filler neck that rose in pitch from the escaping air as the tank filled and stopped whistling when it was full, at which point the gas jockey would stop pumping gas. By 1953, or maybe '52, the whistles were gone, probably because automatic shutoffs had made them obsolete. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 1, 2015, 9:46am UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/18 "2015-01-01T09:46:12Z")
> [@Kenm](#): > > Not true. Pumps shut off suddenly all the time when vehicles’ gas tanks, or even gas cans, are nearly full. They’re built to do so, to prevent over-filling and spills. > > Back pressure on the nozzle, I presume. > > My parents’ '51 Chevy had a whistle in the gas-tank filler neck that rose in pitch from the escaping air as the tank filled and stopped whistling when it was full, at which point the gas jockey would stop pumping gas. > > By 1953, or maybe '52, the whistles were gone, probably because automatic shutoffs had made them obsolete. The automatic shutoff in the nozzle it a mechanical pressure activated thing though, isn’t it? Shutting off the flow abruptly at the nozzle is easy, stopping the flow at the pump at a certain value is not too hard either, but those two things aren’t the same thing. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [January 1, 2015, 11:33am UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/19 "2015-01-01T11:33:52Z")
> [@Kenm](#): > > It does when it’s 30 below, either temperature scale, with a strong wind. Or even in summer with the wind making the rain horizontal, so the roof over the pump area is meaningless. Anyway, it’s more like 30 seconds, not three. > > It doesn’t happen only with cash payments. The pumps slow to a crawl with debit-card purchases and the max price punched in. #firstworldproblems ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [January 1, 2015, 2:21pm UTC](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547/20 "2015-01-01T14:21:09Z")
This thread raise an interesting question. How many people just hang up the nozzle and leave when the pump slows down? Similar to people just dropping change on the ground at a drive thru. I’ve always waited until the pump shuts off. But someone could just leave and not get that last 75 cents worth of gas. At todays prices (2.10 a gallon) thats less than a half gallon. [Next page](https://boards.straightdope.com/t/gas-pumps-slowing-down-when-you-get-close-to-the-purchase-price/708547.md?page=2)