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Discussion Starter · #1 ·
I have a feeling that my dealer didn't fill my tank up all the way even though the meter says it was full. The reason:

Tank 1 MPG: 38.11
Tank 2 MPG: 49.33
Tank 3 MPG: 47.17
Tank 4 MPG: 49.86
Tank 5 MPG: 49.65

I didn't drive that much different between the first 2 tanks. Anyone else see low MPG for the first tank and much higher MPG for tanks after the first one? It looks like I was short approximately 1.12 gallons on the first tank. If the dealer(s) did that on every car sold they could save a ton of money.
 

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It wouldn't have had anything to do with how full the tank was. It would more have to do with the car using gas and not moving very much, perhaps for some PDI stuff or something like that. Also, the car takes a while to achieve its maximum mpg.
 

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Discussion Starter · #3 ·
redwein said:
It wouldn't have had anything to do with how full the tank was. It would more have to do with the car using gas and not moving very much, perhaps for some PDI stuff or something like that. Also, the car takes a while to achieve its maximum mpg.
Not true. Let's say the tank isn't completely full when received from the dealer. I drive 400 miles and fill up. Lets say I fill up 9 gallons, so my mileage is 44.44. However, if the tank was filled up all the way from the dealer, then I only would need to fill up 8 gallons, so my mileage would be 50 MPG.

That's what I think happened, but I admit that I did fool around with the car idle when I first got it, but it seems like 10 MPG lower is a little much.
 

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uclabruins said:
Not true. Let's say the tank isn't completely full when received from the dealer. I drive 400 miles and fill up. Lets say I fill up 9 gallons, so my mileage is 44.44. However, if the tank was filled up all the way from the dealer, then I only would need to fill up 8 gallons, so my mileage would be 50 MPG.

That's what I think happened, but I admit that I did fool around with the car idle when I first got it, but it seems like 10 MPG lower is a little much.
It is true that you can't do a computation if you don't zero the mileage out when you fill up, since you don't know how many miles you have actually driven since the tank was full, but that is obvious. It isn't that the car got worse MPG. It's just that you don't have accurate data to do any computation.
 

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Discussion Starter · #5 ·
redwein said:
uclabruins said:
Not true. Let's say the tank isn't completely full when received from the dealer. I drive 400 miles and fill up. Lets say I fill up 9 gallons, so my mileage is 44.44. However, if the tank was filled up all the way from the dealer, then I only would need to fill up 8 gallons, so my mileage would be 50 MPG.

That's what I think happened, but I admit that I did fool around with the car idle when I first got it, but it seems like 10 MPG lower is a little much.
It is true that you can't do a computation if you don't zero the mileage out when you fill up, since you don't know how many miles you have actually driven since the tank was full, but that is obvious. It isn't that the car got worse MPG. It's just that you don't have accurate data to do any computation.
Yes, I don't have accurate info for my first tank, so my first tank mileage is off and that affects my overall mileage too.
 

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You need to clarify whether you are going by the mpg reported on the screen or doing the actual based on miles driven and gallons filled. If you had hit reset it wouldn't matter whether the tank was full or not. If you dividing miles driven by gallons filled it would.

PA P
 

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Discussion Starter · #8 ·
PA Prius said:
You need to clarify whether you are going by the mpg reported on the screen or doing the actual based on miles driven and gallons filled. If you had hit reset it wouldn't matter whether the tank was full or not. If you dividing miles driven by gallons filled it would.

PA P
I went by calculating miles driven by gallons filled.
 

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uclabruins said:
I went by calculating miles driven by gallons filled.
That's actually a lot less consistent than using the MFD computation, which is based on fuel injector cycles. Some will argue that it is more accurate averaged over a long time, but the car's computation will give you a better relative measurement of whether this tank is better or worse than the last one. The problem with the "standard" method of calculation is that the fill level from one fillup to the next is not consistent. This is probably true of most cars, but the fuel bladder in the Prius seems to exaggerate it.
 

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first tank of gas on new prius

I remember now that my tank was at least two pips short of being full when I drove away from the lot, but I didn't realize it until later. It should have been full because that was part of the package I paid for. My mileage for the first couple of tanks was not great for the reason someone else mentioned, I had not learned to drive to get the best mileage. Even driving like I did my old car, I still get twice as much mpg. However, to get in the high 40's, 50's on the MFD, this is what I do: Set one of your trip odometers every time you take your car for a spin, or for a certain period of time. That way you can remember if that mileage was mostly highway or city driving, and you can see if that has made a difference. I live where there are a lot of hills, and using cruise control on the highway is not necessarily a good thing because if I am not in a hurry and no one is behind me, I can slow down for better mpg. The cruise control will push the engine up to the speed set even going up those hills. I do get better mpg in the city. I have even learned an alternate route out of my own neighborhood that is just as short but without all the stop signs. It has some curves and yield signs, but I coast around those at 99.9 instead of having to stop and start several times for the first 5 minutes of my drive.
 

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first tank of gas on new prius

I remember now that my tank was at least two pips short of being full when I drove away from the lot, but I didn't realize it until later. It should have been full because that was part of the package I paid for. My mileage for the first couple of tanks was not great for the reason someone else mentioned, I had not learned to drive to get the best mileage. Even driving like I did my old car, I still get twice as much mpg. However, to get in the high 40's, 50's on the MFD, this is what I do: Set one of your trip odometers every time you take your car for a spin, or for a certain period of time. That way you can remember if that mileage was mostly highway or city driving, and you can see if that has made a difference. I live where there are a lot of hills, and using cruise control on the highway is not necessarily a good thing because if I am not in a hurry and no one is behind me, I can slow down for better mpg. The cruise control will push the engine up to the speed set even going up those hills. I do get better mpg in the city. I have even learned an alternate route out of my own neighborhood that is just as short but without all the stop signs. It has some curves and yield signs, but I coast around those at 99.9 instead of having to stop and start several times for the first 5 minutes of my drive.
 

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PS about setting trip odometer

I think what I meant to say was also to reset the mpg display on the MFD itself when you reset your trip odometer. That MPG display doesn't reset itself I think unless you refill about 10 gallons of gas. But if you always write down how many gals of fuel you buy and what your odometer reads anyway, like I do, then you can compare the total tank mpg in the long run.
 

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Yeah my tank was not full also at receipt but I did not notice until I was 20 miles away and figured oh well. Short 2 gal back then was about $6. My first tank MPG was 49 something and then the subesquent tanks were 57ish. It still annoys me to see that blip on my spreadsheet. :p But the lack of data was annoy me even more.
 

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I noticed a similar thing with my new Prius. However, when I was at the dealer the salesman had the car on while he proceeded to show me all the features..and I mean all of them. Then after I got home I had the manuals in front of me while I programmed things into the dvd navigation system for a while, tried out the iPod, etc. So I figure it happened because of a lot of idle time having fun with my Prius.
 

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Yeah, I'm sure most people won't read forums like this until after they get the car, I would recommend IMMEDIATELY filling up after taking possession, and resetting the MFD's mileage meter. Ignore mileage results for before you fill it up; as you can't be sure how full the tank was. (Other possibilities include the dealer doing all their preperations will have the car on without moving very far, so it will likely burn alot more gas than the normal user would use.)

When I take mine in for any kind of service, I keep track of what the mileage meter said when I go in, and what it says when I leave. Almost invariably, it comes out noticably lower. (One time that I filled up immediately before dropping it off, I was able to calculate that they used 1/3rd of a gallon of gas going less than 2/10ths of a mile. That'll kill your mileage for a tank.)
 

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On the contrary, I'm noticing just the opposite, my mileage was 49 with my last two tanks and this time it's is less than 41, I wonder why that is...mebbe the cold is playing a part....
 
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