Why don't you fill the tank all the way up. Record how many miles on are on the odometer. Run the car as you normally would, and when the tank is nearly empty, fill it back up, and take note of how many gallons you just put in. Record the odometer miles again, then figure out how many miles were driven. Divide the miles driven by the number of gallons of gas you put in. This will give you your MPG.

How many miles per gallon did you get?

It's possible there is nothing wrong with your fuel tank. You may have a bad fuel level sending unit, or you may have corroded wiring between the fuel tank and the fuel gauge, so your fuel levels aren't reading properly all the time.

 

Basically agreeing with the above mentioned. I'd say to pull out your fuel pump and inspect the coil on your fuel level sending unit. Also look for any debris or contaminates in the bottom of the tank that may cause corrosion or malfunction of your sending unit. Obviously if there is get it cleaned or replaced My Celica does the same.. Burns out the first half super fast and then my last half gives me 200 plus miles.. Get an extra 5 gal. tank of gas to pack when you get to 1/4 tank. I think you may have to Run it dry (not with a dirty tank) to know for sure and see if you get an adequate amount of miles that you would expect for 1/4 tank. If your getting Probably 60-80 miles before running out of gas then your gauge is right.. any large amount of mileage more your sending unit is reading incorrectly. I get about 300 to a tank I don't know if that is standard but that's what i get. A good starting point I suppose.

 

Yeah, I get about 300 miles to a tank when doing mostly city driving. When on the highway, I can get 400 miles or more to a tank (never got 500 miles on a tank yet).

On my gauge, it seems pretty linear. I would say I get have the total miles I will get on a half tank when the gauge is reading 1/2. So why some gauges drop the first half quickly, then slowly on the second half, I'm not sure why that would be.

 

Did that the first day I noticed it and it is getting out from somewhere... No way this little GTS should be topping off at only 130-150 miles off a full tank. Which is what you get if you fill it full and go by the trip meter when the light goes on and it dings for gas.

And did the math by what I got average at the quarter mark on the gauge it does come out more correct.. 250-300 miles as a quarter tank will run about 65 miles from the mark before it dings and you get the light. and as gar as I can tell its a 15 gal tank?

First place I looked was all around the fuel tank, pump & all the lines (pretty much every thing you can see visually while the car is standing still anyway)

The tank is kinda crusty on its outside from sitting. I would be pretty confident that if the tank is leaking I would at least see a wet spot somewhere.. or at least smell it and considering the mileage per tank I'm getting I would think it would be a pretty good size leak... I used to have an old S10 pickup truck eons ago that had a leaky tank and it was plain as day, 1 call to the local bone-yard, 2 weekends, new used tank & drove it for 10 more years & 150,000 miles until my kids killed it...

Seems whatever it is doing and wherever it's mysteriously going to it only does it while its in moving. Kind of worried that this GTS is going to turn into a rolling mallatof cocktail at 65mph on the road... either-way I did put a fire extinguisher in the trunk until I figure this out...

 

I'm not exactly sure what you just said, Onebadbug. What is your fuel mileage (MPG) on your GT-S?

 

You cant always take the ticks on the fuel gauge for being accurate. They're an estimate but are rarely exact.

 

all the math is in there...

Looks like it holds aprx. 15 gal of fuel to fill the tank... though I haven't run the tank dry but from its lowest reading after the light being on and dead flat on the needle twice now both full fills were about 14 gallons and some change. So if this is accurate then yes it has a 15 gallon fuel tank.

If you go by these full tanks going on Avg. 140 miles from full until the light for gas comes on then divide by 14, (guessing at -1 gallon for the reserve light coming on) you get loosely less than 10 mpg on average based at a full tank...

But now when the tank is at 1/4 of a tank roughly 3.75 gallons, and yes it's gauge seems pretty accurate and also confirmed this by that its near exact from what it takes to put in it according to the fuel pumps counter also and reads exactly to the high side of the 1/4 hash mark on the cars fuel gauge.

Seeing as it all seems to match up then the 3.75 gallons I put in & when you do the math from this I am getting on avg. 70 miles until the light comes on so divide by 3.75 I am getting double the mileage, round it up, 18 mpg

So...
From a full tank I average less than 10 mpg
From a quarter tank I average greater than 18 mpg

Seeing I average greater than 24 mpg in the '92 300Z... And is also why I put the fire extinguisher in the Toyota's backseat until I find the problem. Something is, without a doubt, leaking or eating fuel somewhere.

Just wish it was dripping on the ground or something was wet with fuel... or I could smell it somewhere... Nada, Nothing anywhere... yet...

 

Wow. Assuming you have a 5th Gen Celica GT-S with the 5S-FE. You should be getting in the upper 20's in the city, mid 30's on the highway.

If leaking, you should be getting a strong odor, especially if parked inside a closed garage. Parked outside may be more difficult to notice. Don't know how many days you go between full to empty on a tank, but if only a few days, I would expect to see some wetness somewhere, because this seems like a major leak. If the engine is running this rich, you should have black smoke coming out of the exhaust, and the engine likely would not be running very smoothly.

Wouldn't hurt to have the engine running, and follow the fuel lines from the tank to the filter, to the fuel rail, to the pressure regulator, and back again, to see if you might have a pin hole leak somewhere that is misting the fuel out when running.

The fuel has to be going somewhere (either being burned, leaking, or being lightly misted out of a bad fitting, hose, metal tube, filter, or out of the fuel tank itself).

 

someone is siphoning your gas! put a lock cap on it lol