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Please Help, I am a newbie and know nothing about cars

I own a Ford Contour, I believe that it is a 2005 or 2006 model, possibly 2007. Anyway, in addition to the typcal needle based “Empty -Full” fuel gauge, the car’s dashboard provides me with a digital estimate as to the number of miles I have left in my gas tank. I filled up my tank a month ago, and the car told me that I had 403 miles to go until Empty. I assumed that this meant that my tank held 403 miles worth of fuel. A week later, I filled up again (same gas station, same type of gas) and the readout told me that I had 389 miles worth of gas in my tank. A week later after filling up, the readout told me that I had 375 miles worth of gas, and when I filled up this past week, it told me that I had 350 miles worth of gas in my recently filled tank. I am starting to get both worried and annoyed. I understand that the readout isn’t “exact”, but sweet Jeebus…how can this figure vary so drastically, when I am filling up the tank at the same station, with the same type of gas each week? It doesn’t make sense. I full tank of gas this week is only worth 350 miles, whereas 3 weeks ago, it was worth 403 miles??? I don’t get it. Can somebody help me out please? Thanks.

Simplest explanation would be gas millage is dropping. Are you due for fuel filter, air filter, plugs, oil change etc?

It wouldn’t be a 2005,2006, or 2007 as the Contour went out of production in 2000. I doubt if anything is wrong. It’s entirely possible for it to read 350 miles in city driving then guesstimate over 400 miles till empty after run on the freeway. Since the estimate it’s giving you is based upon the last 30 miles or so of driving.

If it annoys you, put a piece of black tape over the offending readout and drive on…

FoDaddy's explanation is a good one. My 2010 Cobalt and my wife's 06 Sienna both have DTE readouts. When DTE = 0 on my wife's Sienna, there is about 3 gallons left in the tank. As far as I can tell DTE = 0 on the Cobalt means the tank is empty, I don't let it go below DTE = 90 or roughly 3 gallons left.

The DTE readout on the Cobalt usually reads about 20 miles higher than when I parked it. After a few minutes of driving the DTE drops down the 20 miles. Under highway conditions the DTE will sometimes increase due to the increased mpg. I consider the DTE an estimate, nothing more.

To determine mpg, note the odometer reading and amount of gas at each fillup. After 3 or 4 fillups (~1000 miles), divide the mileage by the total number of gallons to get the mpg. The Cobalt and Sienna both have average mpg readouts, but I still calculate mpg based on distance and gallons used.

By the way, are you sure it's a Contour? Open up the Owner's Manual, it will explain this better than I can.

Ed B.

Thanks, guys. I appreciate the responses. You are obviously correct-I was mistaken when I referred to it as Contour. It is a 2007 Taurus. I apologize for the error.

So, if I understand the responses correctly, the DTE bases it's "readout" on the 30 or so miles I drove immediately before I pulled into the gas station to fill up? That is, its estimate is based on the type of gas mileage I was getting most recently? I know that you get better mileage on highways than in stop and go city maybe the days when I got the highest DTE readouts after filling up (the 403 and 389 miles to go before Empty readouts) were days where I had been driving on the highway immediately before I pulled into the gas station, and that is what accounts for the increased DTE reading? Is that correct or did I misinterpret your posts?

I think you nailed it. The gas mileage is calculated using the most recent driving. The amount of fuel going in the tank is the same. If you do a lot of city driving your DTE will start to go down at each fill up. Conversely, if you go on vacation and spend all day on the highway you will see the DTE number go up at each fill up.

The OP should bear in mind that the onboard computer that provides gas mileage estimates is not a laboratory-grade instrument. It should be used to approximate one’s current gas mileage and the number of miles left in a tank of gas. Relying on it to a major extent could provide some unpleasant surprises–which is why it is not wise to get into the habit of waiting until a gas gauge reads “almost empty”. The gas gauge and the digital readouts of gas mileage and miles to empty are never precise.

As to the make, model, and model year of the car that one is driving, there is an extremely simple way to figure out this information: Look at the vehicle registration which should be sitting either in your glove compartment (not a good place) or in your wallet (the preferred place).

Torretta13 , Don't Know Make / Model / Model-Year ? . . . Just Curious (And To Settle A Bet) , What Method Do You Employ To Locate Your Car In A Parking Lot ?

Do You Use Color, License Number, Unique Window Sticker, Strategic Body Damage, Antenna Flower / Mickey Mouse Head, Remote FOB To Make Car Chirp . . . None Of These Or A Combination Of Some Of These ?




I think it is doubtful that the OP would use the license plate number as an identifier of her car. If she doesn’t know the model year or the model, what are the chances that she would know the license plate number?

Perhaps this explains those cars I see at the mall with a big artificial flower on the antenna.

Thanks for the help and advice, guys. I appreciate it. Your responses regarding why my "full tank" DTE readouts would fluctuate so wildly makes a lot of sense.

As for the last couple of comments....hardy har-har. Everyone's a comedian these days.

All it is doing is looking at the average miles per gallon since the last time you reset it, looking at how full the tank is, and doing the calculation of how far you can go. This is something I very rarely even look at since I don’t let the tank get less than half full and have never relied on the calculation for much of anything. Computers are smart but also dumb. It just does the math.

Yes, those digital readouts take a while to adjust when going from highway to city driving and vice-versa. They take much longer to adjust when recalculating themselves from city to highway MPG and this is reflected in the miles to empty, etc.

Those readouts are controlled by a module that takes info from various sources and they even have an anti-slosh circuit in them to account for fuel slosh in the tank. A problem in the tank or module can also cause variances.

My LIncolns have something like this and they’ve always been prone to going stupid for a few days about once a year.
In the latest example of going stupid it went stupid and stayed that way. With an 80/20 mix of highway/city driving the readout shows 24 MPG and about 440 miles to empty from a full tank. In reality, the car is getting 27.7 MPG and the miles to empty should be about 480 or so on a full tank.

Mine doesn’t do so well, until you’re down in the 1/4 tank area. Every tank it tells me I’m gonna get somewhere over 400, but that’s a flat out lie. I normally hit somewhere around 380.