first half of gas tank goes down quickly?

Question

Why does when I fill up my gas tank, the first half goes down quickly, but the second half of my tank goes down slowly

Answer 1

Gas gages are rather inaccurate.The shape of the tank near the top also could cause this.The real answer here is what is your mileage? (mpg) If it's about what is should be then only worry about when you should fill up.I also assume that you dont smell gas or have a leak near the top of the fuel tank since you didnt mention it.

Answer 2

Your fuel gauge is more or less just a relative indicator of the fuel level in the tank. It uses a float on and arm that is attached to a variable resistor. As the level, and thus the float, drops the resistance changes and the gauge indicates the change.

What is generally not taken into account is that modern fuel tanks are not consistently shaped. They are essentially molded to fit in whatever space there is under the vehicle, so the top may be smaller than the bottom, or vice versa. As fuel is used, the level may drop slower or faster depending on how wide the tank is at that particular point. Think along these lines: if you took a 1/2 gallon milk jug and a one gallon jug and filled then both to the top; both fill levels would be at about the same height off the table if you put them next to each other; now punch equal sized holes in each one ( say about 1/4" ) near the bottom and drain out 1 quart from each jug. The 1/2g jug's level would be lower now because it is narrower and therefore held less fluid.

So that is the main reason why your gauge moves at different speeds. Where the tank is narrower fuel level will drop faster than where it is wider. It sounds like yours is narrower at the top. Automakers could build a computer module that could use the level sensor and algorithms to give a more accurate reading of fuel quantity, but that would drive the price of a new vehicle even higher.

If you want to calibrate your gauge yourself, simply fill the tank to the same point each time you fiill up ( one click on the pump, say ), and drive as normal as you can. Once its almost empty, fill up again and divide total miles travelled on that tank by the gallons needed to fill up to get fuel MPG, then you can determine when you are at 3/4, 1/2, and 1/4 tankful by the miles travelled since you last filled up.

I hope this answered your question alright. Good luck.

Answer 3

The shape of your gas tank determines how quickly the gauge drops. All the gauge does is measures the level of the fuel in the tank, not the volume.The only way your gauge would drop at the same rate from full to empty is if your tank were the same shape from top to bottom. But automakers have to make fuel tanks in odd shapes to make them fit. On some cars, the first half drops slowly, and the second half drops quickly. Take a look at this website. http://www.dicksautoparts.com/Shop/Gastanks.html See how the tank tapers smaller down toward the bottom? This baby's gonna drop slow the first half and fast the second half.

Answer 4

There are several possibilities.

1.A hole in the tank positioned near the top.
Look for liquid leaks below your car. This could be very dangerous. and will likely require a new gas tank as soon as possible to avoid explosion and fire.

2.The intentionally designed variation in the gas gauge readings. Manufactuerers do decide how they think buyers of their cars 'want' their gas gauge to operate. Somehow, "accurately" and "consistently" is not the goal.

3.The variation in the shape of the top of the gas tank to the bottom. If the top of the tank is narrow, it would not take as much gas use to lower it in that level of the tank, then perhaps the tank is wider toward the bottom of the tank, it will then take longer to use one inch of liquid fuel in that level of the tank.

It might be best to check your overall gas range, or mileage per tank of gas. Keep an eye on that, with awareness that driving conditions and drivers do change. Keep the car well tuned,and the tires properly inflated. This can help you determine whether you gas milage is really changing or whether it is simply the design quirks of the fuel level guage, the readout guage on your dashboard, or the design of the fuel tank.

Answer 5

I have this theory that works for me, but many people nay say. It is a purely mathematical equation. Your engine is the driving force of your car, that supports everything else in your car. Have you ever noticed how if you have 3 friends in your car opposed to just you how your car bogs down and just doesn't feel the same? Well its the same with a full tank of gas. The more gas you have the heavier your car is, therefore increasing the amount of gas required to support the car. Your car is running at a higher RPM and burning more gas to transport the gas weight. It may sound ludicrous but really it's not. Keep your tank at half and notice the difference.

Answer 6

First thing check to make sure u not leaking gas. If that's not it change ur fuel gauge n the gas tank. Some r a float gauge, attached to the bottom of the tank. Look at ur owners Manuel n it'll tell u where its located at exactly n what type it is. Good luck

Answer 7

Depending on how old you card is if the floadter in the tank is getting stuck on the traveling rail do to rust it will come loss with the gasoline splashing.

Answer 8

You have a hole in your tank. see if there are any stains in your driveway or else the smell of gas around your car always. VERY dangerous

Answer 9

if you have a gas leak you will smell it. the gas gauge in my truck and my wifes car seems the opposite. all my cars have been opposite actually. it always seems to go down slowly till it hits halfway then it seems to go faster.

Answer 10

may be a off balance in the tank of ure engine may take more to get going and less after it runs a while.