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MPG drops after 1/4 tank?
After I fill up my gas gauge barely moves for the first 100 miles or so, But after that it seems to drop really fast and I'll end up getting like 300 miles out of a tank. To test this I filled up and drove for about 80 miles and averaged like 28 mpg. Then refilled the tank and drove for about 280 miles and averaged about 23 mpg.
Same driving style. Same terrain. The weather was similar, etc.
BTW I drive a Kia Spectra and these MPG ratings are horrible compared to the EPA estimates but I've experienced similar gas needle phenomena in other vehicles. Any thoughts??
7 Answers
- Allan CLv 61 decade agoFavorite Answer
When your tank is full it is actually over full. So you probably drive the first eighty miles or so before the gas guage is actually at the full mark. The float can only go up so high and the gas guage can only read the amount of gas when it is so high. When you fill up the tank you take the float as high as it can go and the fuel is above that so you have to wait until the fuel level drops down to where the float is actually floating on top of the fuel to get an accurate reading. I hope this made a little sense.
- 1 decade ago
The gas gage issue is common on most cars and trucks. This is because of the shape of the gas tank and how a sending unit works.(the sending unit is the gizmo inside the tank with a float attached that sends the signal to the gage in the dash) That float goes only up and down, no matter what the shape of the tank is. Now, think about an upside down triangle where the point is on the bottom. If that's the shape of your tank, the bottom half will have a lot less volume than the top half of the triangle. using a gallon of gas from the top of the tank will not make the float move much, but using a gallon from the bottom will.
Regarding mileage ... I suspect when you fill your tank you are not filling it the same amount each time. If you fill it just till the pump shuts off automatically, you will definitely get a wide variation in fill level. On my car, depending on the pump I use, I can get as much as 2-1/2 gallons more in after the auto shut off.
- Anonymous1 decade ago
The gas tanks are not regular shaped and you can not gage the top 1/4 tank and from the bottom.
Fill up the tank and drive xx miles, Fill up and drive the xx mil;es then set the tripmeter and drive xx miles then drive to the bottom quart and drive xx mile.
You will find that xx mileage is the same regardless of which part of the tank it comes from
- 1 decade ago
If you overfill the tank then the needle will stay up above full for a bit then drop. Also, maybe the car drinks more fuel when it gets hot. There are many scenarios.
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- Brian SLv 51 decade ago
It's the way your gas tank is shaped verses how your fuel sending unit drops with the fuel getting lower, a decent auto manufacturer usually makes sure it is accurate all the way down.
- 1 decade ago
Its because your kia has 18's but you tell the ladies that they are 20's.
or the shape of your gas tank .. hmmm interesting.
