Window Sticker Car Miles Per Gallon

    (Getty Images)

    by: Terry Shea | AOL Autos

    Today’s cars are packed with high-technology features throughout. From the latest overhead-cam, turbocharged, direct-injected engines, to slick-shifting, computer-controlled twin-clutch transmissions, to voice-controlled infotainment systems with more computing power than it took for the Apollo program to put a man on the moon, there is virtually no area of a modern car that has not benefited in some way from these advances.

    Except for maybe the gas gauge, that is.

    With a plethora of integrated, microprocessor-controlled systems throughout the car, delivering countless calculations per second regarding speed, throttle position, temperature, fuel mixture, the car’s attitude to the road and even navigation systems that can pinpoint your location within 100 feet no matter where you are on the planet, the ordinary gas gauge continues to give you -- at best -- a vague estimate of how much fuel you have in the tank.

    Giving The Customer What They Want

    Have you ever noticed that your gas gauge stays on full for quite a while before the needle even moves and then it moves faster and faster as it approaches empty? And then when it gets to “E” it sort of stays there for a while until the low warning light comes on, which might even be accompanied by a friendly chime, just in case you didn’t get the visual memo that it’s time to fill up?

    It turns out it’s partially your fault that gas gauges work that way.

    The engineers calibrate them to do that. Why? Because you, the customer, have told them that’s the way you like it. We spoke with Phil Pierron, an engineer at Ford (his title is actually “Technical Expert for Systems Engineering in Core Fuel Systems), who told us, “Our customers really didn’t want to run out of fuel when they hit ‘E.’ Customers do want some amount of fuel when they get to ‘E.’”

    Apparently, consumer surveys indicate that people don’t like seeing the needle depart from “F” right away either, which it should technically do the moment you leave the gas station. According to Pierron, “[Customers] want it to say on full for an amount of time.” This gives them the illusion that they are getting better fuel mileage or at least not immediately burning through that expensive tank of petrol they just bought, even if they quite literally are. And just as you have a “reserve” that kicks in after you hit “E,” the engineers call this stickiness on the “F” mark a “full reserve.”

    Whatever Happened To Accuracy?

    If fans of accuracy were giving out grades, they just might give that attitude an “F.” The very idea of “calibrating” a gas gauge to assuage our feelings toward our car is akin to setting your clock ahead 10 minutes so that even though you know it’s 10 minutes fast, it somehow motivates you to get out of bed earlier, when in reality all it does is encourage you to snooze away that extra ten minutes anyway. The difference with the gas gauge is that those 10 extra minutes are not optional on the driver’s part. We are stuck with gas gauges designed to make people feel better, not accurately report the level of fuel in the car.

    While customers want there to be a “reserve” of gasoline available when they reach the empty mark, but there isn’t technically a reserve tank, there’s simply a real empty point that is not marked on the gauge. At the same time customers don’t want too much of a reserve. Otherwise, they will complain that their 20-gallon tank only takes 15 gallons when filling up from empty. Apparently, there is a sweet spot where customers are happy to be fooled by their gas gauges, but not too much. We customers sure are a fickle bunch.

    The engineer’s job should be to make things more accurate and efficient, but in this case he has to play psychologist to keep customers happy.

    In defense of the engineers, gas gauges do need a bit more calibrating these days since the tanks, particularly on passenger cars, are often oddly shaped to fit around the various parts and fill spaces in their allotted areas underneath the chassis. They also have to meet crash, temperature and emissions requirements.

    The Un-measurable Top-Off

    Santo Spadaro, an experienced mechanic who grew up in the family business, Domenick’s European Car of White Plains, New York, doesn’t necessarily see the gauge as inaccurate, but with an impossible task in determining what’s full. Spadaro points out that, “Beyond the gas tank, if you top it off, you end up with three-quarters of a gallon, maybe a full gallon, of extra fuel [in the filler neck]. So, it seems that first quarter of a tank you are getting sensational fuel economy.” He also points out that he usually tops off his tank with a few extra pulls of the gas pump even after it reaches the automatic stopping point because he likes to keep those trips to the gas station to a minimum.

    Ford engineer Pierron also has a difficult task on his hands when calibrating for that top off routine, as it can be difficult to accurately measure. All gas pumps are not created equal, so one pump might give you a few more tenths before shutting off than the next pump. And some customers may pull the nozzle when it stops the first time, while others may keep going until the gas is splashing out onto the ground.

    Calibration also helps the gauge stay steady when you are on a steep incline, on a twisty road or when you park the car in an unusual position. Even with a half tank of gas, you might see full or empty the next morning when stepping into the car if the gauge is not calibrated to factor the car’s attitude into the equation.

    Repair Estimator

    Old School Technology

    Curiously, while the technology clearly exists today to give every driver a very accurate reading of the fuel in the tank, the actual mechanism that measures the fuel in the tank has changed very little in the past few decades. Spadaro, at whose shop you are just as likely to see a classic Alfa Romeo or rare Lancia from the 1960s as you are a modern BMW or Jaguar, has seen them all and agrees that the sending unit really hasn’t changed much. “Generally, they’re all created equal and they’re all variations. It’s a lighter-than-gas float and a rheostat,” says Spadaro.

    In the old days of simple electro-mechanical gauges, the accuracy of the gauge was usually thrown off when the tank was near full and the float might be submerged for some amount of time as the fuel gets used or when the tank was near empty as the float might reach its lowest point even as various nooks and crannies in the tank might still have gas in them. Today’s microprocessor controlled gas gauges could easily clear up those discrepancies, given the engineer’s ability to program them out when calibrating the gauge.

    Here’s an idea for the next-generation of fuel gauges, particularly now that instrument clusters are largely being replaced by single-panel LCD units: Give the driver the choice. How about a button to switch between an accurate readout and the “feel good” calibration? And then let it synch the dash clock to ten minutes faster at the same time.

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    1 - 20 of 128 Comments
    Henegizer Dec 23, 2010 5:54 PM
    I live in Minn., and I'm astonished at how few full-service stations exist anymore. Luckily, there is a Standard Oil service station just six blocks from my home, and it's full-serve...at the same price as the self-serve station across the street! The attendant pumps my gas, washes all the windows (including side windows), checks oil and other fluids, and puts air in the tires. Believe me, in a state where the temperature drops to 40 degrees below zero, it's nice to stay in your warm car while someone else does all the work! Very few "service" stations exist anymore; what we have are "gas stations" where you do everything yourself, then pay inside to a clerk who does nothing but sit on a chair and eat candy bars and soda all day. How sad. Incidentally, my 1965 Ford Mustang has a more reliable gas gauge than my 2007 Mustang...go figure!
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    CMax383666 Dec 22, 2010 10:04 AM
    Lets move on.Cars are not built for anything but costing money .We are getting so caught up in the latest fad or details that the picture is geting lost. Another way of putting it americans are getting so focus they cannot see the forest for the trees and pretty soon they will not be able to drain the swamp because of all the alligators that have been ignore until it is too late.The shape of the tank alone makes it hard to track exactly how much fuel you have left and how much are you willing to pay to know exactly how much fuel you have left or used.This problem is not a problem it is a ruse to avoid or support the price of automobiles.The electric cars will take care of most of that issue be them hybrid power or only electric.,By the way what do do think the pwr companies are going to do when there are say 20 to 30% plug in electric cars on the road. Henry Ford and one other person built are car in history for working class one was an American and one was nuts.
    Report This
    uaoz Dec 21, 2010 5:40 PM
    alot of dumm people here,,,,,,
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    VLADY1000 Dec 15, 2010 11:45 PM
    As a kid, I remember my dad's old VW with no gauge, but it did has a real reserve tank. Head lights were likedriving with 2 flashlights and a defroster that almost, barely blew luke warm air in the 2 lower corners of the windshield (we use to scrape the inside of the windows (while driving) more than the outside. Always ran and always went thru the snow.
    Report This
    cloveyarnell Dec 15, 2010 7:08 PM
    What gets me is ,most of the people here can't spell gauge right..... hahaha lol
    Report This
    jjoss Dec 15, 2010 1:50 PM
    Inaccurate gauges are not only deceptive but dangerous. Deceptive readings mean that ******** up a rental car or truck with the gauge reading 'Full,' drive it 20 miles and put four gallons in when returning it, because the previous driver didn't and the rental company didn't top it up and charge him or her. Dangerous, because you can be deceived on a long drive by getting 'such good mileage' from the first half tank and multiply that by two for the full tank, except that the first 1/4 tank gives you 150 miles, the second 1/4 gives you 100, the third quarter delivers 50 miles and then you're almost on reserve. If this happens late at night in bad weather on a lonely road, you could die. My motorcycle has a gas gauge and it read precisely. It can be done. Car makers should do it, But the author of the article was not able to muster these aspects of the problem. Sad.
    Report This
    mrshonl Dec 15, 2010 10:35 AM
    I get gas when I go to a Mexican Restaurant
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    bondsupply Dec 15, 2010 9:01 AM
    As an owner of many different cars through the years ,also motorcycles and boats ,I have always filled up when I am down to about half a tank ,especially with the newer cars ,most cars now have the fuel pump in the gas tank and the fuel also cools the fuel pump and by doing this you also dont suck up any dirt from the tank . I also dont get gas when the station is getting a delivery because it turns up the dirt in their tanks .
    Report This
    wrascil Dec 14, 2010 10:04 PM
    the first white dot by empty means fill up now, the lower white dot means get out and pushhhhhh
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    a3liner Dec 14, 2010 9:56 PM
    The old VW gas guages (early 60s) mechanical ones, were non-linear so that the full part was at a much shorter interval. The last half was stretched out. I found those old gas gauges to be very accurate, including the reserve long arrow. Of course before the gauge there was a valve in the tank. When the motor stuttered, you turned the reserve valve and knew you had a bit over 15 miles of gas left in the tank. Love those old VWs. Ted
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    igroot Dec 14, 2010 9:46 PM
    That gauge might be in liters, as it is in Europe, so if 35 is half a tank that would be close to 9 gallons.
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    dougevchap2 Dec 14, 2010 8:52 PM
    My Lexus 2007 tells me how much cruising range I have. I just went 2 miles past zero and filled up with 17.33 gallons. I subtracted that from the 19.3 gallons that the specs say is the full capacity. Therefore I have a 2 gallon reserve when the cruising range says zero
    Report This
    totalpckge1 Dec 14, 2010 8:52 PM
    What the Blood Clot? Me nah learn not a damn ting yahso.
    Report This
    guerraco Dec 14, 2010 8:15 PM
    Weight of gas in your tank. Not by gallons
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    rshu4you Dec 14, 2010 8:11 PM
    Here's an idea fill your tank when it gets to 1/4 left....
    Report This
    thparki Dec 14, 2010 8:07 PM
    I've had to replace the EVAP canister vent valve on 2 of my cars this year (both were used cars). Both had the check engine light to come on. Also on the first car (truck actually) it caused "extened cranking" to restart the motor after every fueling stop (had to hold the accelerater to the floor while cranking for it to start). The truck had about 107,000 miles on it when it went bad. Cost about $160 to fix. The second car only had 28,000 miles on it and was covered under warranty. The dealer said both were caused from "TOPPING OFF" the fuel tank. They said to STOP filling the fuel tank as soon as the pump clicks/stops the first time. Otherwise you are just forcing excess fuel & vapors into the vapor recovery system and it will eventually cause the system parts to malfunction.
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    sstein2 Dec 14, 2010 7:57 PM
    What a crock. Fuel gauges have acted the same way since the first one was made.
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    ebreit19 Dec 14, 2010 7:47 PM
    Engaging article. Don't run out of fuel or you may ruin the fuel pump and catalytic converter. The gas tanks I'm familiar with hit empty when one has about 2 to 3 gallons remaining so as not to jeopardize things that depend on having some fuel remaining. You can find out the amount remaining by reading the manual when the tank hits empty or by the amount you can fill the vehicle when it reads empty. A 17 gallon fuel tank will only take about 14 gallons, with the remaining amount in reserve. So, one has essentially 17 gallons at each full fill. Also, remember gas expands and contracts according temperature which may give you a feeling of having more or less gas. NTL, one never wants to take a chance with taking a chance of running dry. An average mid-sized vehicle should get at least 300 miles per tank, maybe 360 or more, but that depends on the vehicle and is not worth taking the chance to find out how far it goes on a single tank before running dry.
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    lthrnck68 Dec 14, 2010 7:46 PM
    Want to really know how accurate your gage is? Carry a gas can full with you and run the car until it runs dry. Watching the gas gage while you'r driving will tell you how good the gage is.
    Report This
    puckrj Dec 14, 2010 7:41 PM
    Where do these "writers" come from? How many times can you say the same thing over and over but with different words? Low content to word ratio here.
    Report This
    1 - 20 of 128 Comments
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