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Which fuel level do you trust?

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Dyoel182

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Apr 15, 2008
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North Texas
Which do you guys trust more, the level with the car running or the level after you turn the car off and it stabilizes? Going by my last tank where I let the low fuel light come on and the car took 12.5 gallons (meaning at least 2 gallons still in the tank) I'm more willing to side with the level when the car is off since it reads a touch higher.
 
Not to throw you off but my gauge actually reads less when the engine is off. When I turn it over, the gauge goes up.

IMO I trust the level once it is turned on.
 
Don't trust any of them.

Know what kind of mileage you get (odometer and the amount of fuel you get/use) and go by that.

If your fuel gauge were to stick, break or otherwise malfunction, you're telling me you'd not know? If you don't keep track of mileage then you can't know. you could eventually guess, but you wouldn't know it was broken until you had problems or realized it when you ran out of gas.
 
I USUALLY put gas in my car right at or above 1/4, in the contour 1/4 generally says you have used right around 10 gallons of gas to fill up. So its super easy to clock my mileage, and isn't terribly expensive to fill.

but if I can, I really like to put gas in at about a half tank, filling up doesn't feel as crappy :( but I know it doesn't make any difference. But I always reset my odometer when I fill up, so I know how many miles I went on how many gallons, fuel gauges can be extremely inaccurate for misc reasons.
 
I saw a poster once in a Chrysler stealership....they were talking about how to get better fuel mileage and it was dated back in the early 90's. Basicaly it showed that keeping the tank above half a tank all the time saves you alot of money. So much will evaporate when its lower then that. Expecially on those hot days.
 
The amount of loss would be almost imperceptible, especially in a SEALED tank/system. If your cap is on... where's it going to evaporate TO? (assuming a properly working EVAP system)

There simply isn't any discernible truth to that. In fact, the amount you might have saved (even in an older system) due to evaporation would be NEGATED completely by the fact that you are carrying around an extra half tank of gasoline (5.8 to 6.5 LBS per gallon!!) and that will decrease mileage from carrying around that extra weight.


Bottom line: even IF it would evaporate, and even IF it were enough to NOTICE, it wouldn't compare in the slightest to the mileage decrease you'll get from having that much extra weight.

Its a numbers game, sure.. but if you're getting picky about 1 percent of one gallon then you stand to save much more money from simply carrying around less gas to begin with.
 
98csvt69 said:
I saw a poster once in a Chrysler stealership....they were talking about how to get better fuel mileage and it was dated back in the early 90's. Basicaly it showed that keeping the tank above half a tank all the time saves you alot of money. So much will evaporate when its lower then that. Expecially on those hot days.
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WHAT??????? Where is the gas going to evaporate from? These days all cars have sealed systems anyways and the surface area at half full is the same more or less as at full. I hope you were being funny.
 
This may introduce a different consideration, but I notice a slight fluctuation after turning the car off and then back on again. For example, let's say that the gauge reads 3/4, but then I pull into a Jiffy to get some beef jerky and a pack of smokes. When I come back out and fire up the car, the gauge will generally read a touch lower, usually a needle width.
 
Doesn't the gauge go down to empty when the car is off? :shrug:

I only trust what it reads when the car is running, and on relatively flat ground (I park on a hill).
 
frenchblueC2 said:
Doesn't the gauge go down to empty when the car is off? :shrug:

I only trust what it reads when the car is running, and on relatively flat ground (I park on a hill).
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not in the contours.

but remember when you fill up your tank with your car off (i hope) the gauge will not move until you turn your car on. so why on earth would you go by when the car is off?
 
Like i said guys it was a old poster... heck it mighta even been earlier then the 90's i cant remember. I do notice my car goes forever from full thank to half a tank and then after that it drops like crazy...dose anyone else have this problem???
 
98csvt69 said:
I do notice my car goes forever from full thank to half a tank and then after that it drops like crazy...dose anyone else have this problem???
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lol yeah I've seen people mention this happening to them.
I bet you could dig up some old posts about it.
 
I swear my gauge defaults to 1/2 tank when I shut mine off (assuming I'm below 1/2 already). But I could be nuts. I'm going to have to check this out now.
 
98csvt69 said:
Like i said guys it was a old poster... heck it mighta even been earlier then the 90's i cant remember. I do notice my car goes forever from full thank to half a tank and then after that it drops like crazy...dose anyone else have this problem???
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This can be from a number of reasons:

graduated tanks causing the top to be wider than the bottom
angled floats
or even programming in the fuel circuit to make it go slower for the first half.. Its been done, so its not that crazy..

dacker said:
I swear my gauge defaults to 1/2 tank when I shut mine off (assuming I'm below 1/2 already). But I could be nuts. I'm going to have to check this out now.
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You're probably noticing that when you turn the key to "on" the gauge reads a certain level, but after you start it, it reads slightly different.

This is because you have the pump running, causing some of that fuel to now be in the fuel lines, etc. This causes a slightly different reading in the KOEO vs. KOER positions.
 
Heck when i fill up my gas tank its around 14 gallons, so i take it to the very bottom many times, because iahve acuratly figured out my mileage after 4 years of reading my odometer.

I have always noticed that my tank plummets after it hits the half way mark.

So asof latley i get 180 to 7 gallons and then i fill it back up. If i run it to 13.9-14.2 gallons it ges 320. :shrug:

So to save a bit or get another 40 miles i fill up at half a tank now.

Either way if it helps it helps, if it doesn't then no biggy, i would still have to fill up either way :)
 
98csvt69 said:
Like i said guys it was a old poster... heck it mighta even been earlier then the 90's i cant remember. I do notice my car goes forever from full thank to half a tank and then after that it drops like crazy...dose anyone else have this problem???
Click to expand...
This is a common thing and has been for years. It seems that a lot of people fill at half tank so the perception is that you are getting better milage than you are. I can't say that its intentional but it would not surprise me.
 
Mine can either stay close to where it was while ignition was on, or will go down to 1/4 tank if there's less than 1/2 tank of fuel real world. Also, evaporated fuel gets stored in the carbon canister until engine next started, then engine sucks it out to be burned. There's not a whole lot of loss there, but it IS there. The extra weight of full tank and its' effect on mileage will totally outweigh that loss. The tank reads full before it's really all the way full, i.e., the float is against the upside bump. Fuel higher than that will result in gauge that shows full until high level drops back down into normal gauge range.
 
I trust running level, after about 10 minutes, especially on cold mornings. If I let my car heat up first the gas gauge will increase in proportion to how much is in the tank. More than once I've started my car just under a full tank and shut it off over full...
 
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