I searched for this but could not find anything...



For the past week I've noticed (and remembered) my gas level in the morning , and thevye been conspicuously dropping almost a gallon at times. It dropped a gallon (notch) when I didnt drive the car for 2 days, but it does drop a bit even overnight.

I'm pretty sure it's not thermal contraction or anything like that because I informally keep track of fuel consumption using the gas indicator level at the quarter and half marks and odometer... and after a 2 day hiatus from using the car I lost about 35 miles worth of fuel...

Am I just seeing things or, if not, what is the reason for this?

 

the gas tank is shaped like a saddle bag. the gauge is in one half. the gas is shifted from time to time over the hump. this is the cause of the fluctuation. unless of course you have found a wet spot under the car.

 

but gas left in a car undisturbed for 24 hours shouldnt move over the hump, right?

 

what makes you so sure it isn't thermal expansion/contraction?

Fill up the tank and then let the car sit for a few days, then check it?

 

The gas gauge is not a precise measuring device, it gives you an idea of the level in the tank. The tick-marks on the gauge are likely not gallon intervals and I'm sure the scale changes through the range of the gauge.

The differnce could just be some hysteresis in the gauge making it such that when you turn the car off and it drops down, that it doesnt quite get up to the same level when it's powered back on again.

 

Seems like the best way to be sure to me.

(note this will only work if you live really close to a gas station)
1) Fill up on gas, drive immediately home
2) Let the car stand for a few days
3) Drive straight back to the gas station & fill up

If you're really losing gas, you'll have to put in a few gallons. If not, it'll be like 1/4 - just from starting the car and driving each way.

 

If your car is in a garage I think you'd notice if 35 miles worth (2 gallons?) had escaped the vehicle.

 

if u dont live close to a gas station fill a gas can with gas and fill ur car when u get home lol
if u want to be very sure

 

Maybe somebody got busy with a siphon.

 

Maybe someone is driving your car when you're asleep at night.

 

I too had a drop in gas level overnight. This is what happened. I arrived home from a trip and before turning the the car off I took a look at the gauge and noticed that it was one quarter full. When I turned it on the next morning I noticed that the needle never rose below "E" as if the car was still turned off. The low gas warning light was also on. I had 225 miles on the trip meter but had been driving freeways for about 150 miles of the total. So I figured I'd fill up the tank at the nearest station just to be sure and only filled up 11.74 gallons which netted me 19.5 mpg (Almost 20 but no cigar). Which meant I had another 4.16 gallons left in the tank (15.9 - 11.74 = 4.16). Now the manual does not state what triggers the low fuel warning light but that it only says to fill up soon (My previous car did it at 2 gallons remaining). However, I did notice as I drove to the gas station that the needle did rise slightly above "E" but the warning light never turned off. I'll see if it happens again.

 

I am pretty sure all newer cars have a blocking device for siphons. It did not work for my 2000 Eclipse, my friends 1996 240sx, or my other friends 99 Altima. It felt like we stuck the tube down there far enough, but we were just hitting something before the actual tank.

I can also attest to the fickle gas guage. It likes to speed up and slow down. 20 miles one notch, then it seems like 5 another. I also park my car on a slanted driveway. Whenever I come out and start the car, the gas gauge is usually a little lower, but as soon as I start cruising around town, the guage goes right back to where I remembered it.

 

I have noticed that my gas gauge changes from time to time.

I have parked the car with 1/2 tank with about 135 miles on the odo.
Next morning I had 1/4. This has happened at least three times. Sure enough, I had to fill up @ 180 miles instead of my usual 260.

This occured just after the "L" flash. I have not gotten the "M"

The car is parked inside overnight.

I had Mazda look at it and they found nothing.

 

Just an idea: when you start first in the morning, have your door open and check for gas smell. If anything leaked, the fans should get the gasoline from the engine to you. That would be a small leak in the engine area, hence the hot engine will help evap most of it (so no leak on the ground) but some gas might be remaining under some engine parts, evap overnight, and be pushed by the fan out the first time you start. If that's the case, do see your dealer pronto