Fuel Gage Malfunctioning!!! wt*?

[Alex1]

I filled up monday, i put in like 25 bucks worth, it already had about a quarter a tank or so in it... so the needle goes past full... i put thirty miles on it since monday.. and the guage had been just hitting full, instead of being over it...

so today i went to pick up my friend in the morning, fuel was the same level... i stalled it at the endge of his inclined driveway... so i start it up and look at the guage and it drops to a 3/4 full!! wtf?!?! so im liek wtf... and i restart it and it goes up a little, so we drive and it doesnt change.. after school i look at it and its like half way into the first gallon.. now just now i got out of work and saw that it was like 3/4 or 3/5 the way up on the first quater... im so confused, i dont know if it is reliable now!! what happened!!

 

-alex

[msb175]

yeah, its odd. I noticed that when I park the car on an uphill incline with the front of the car facing up, the gas gauge reads lower. I remember I put filled gas once, went directly to a friends house and parked on his steep driveway. 10 mins later the gas needle came down almost a quarter. Probably cause the car is on an incline, the fuel in the tank is at an angle..... Odd thing is that if the car is parked with the front of the car facing down, the needle doesn't really move....

 

 

Same thing happened on my 95 Explorer that I had. Can't remember if my WRX did it or not though.

[RODMAN]

Hey Alex1 I've had the problem. My driveway is a steap incline and I have had 2 different readings within a matter of minutes. I backed out of the driveway shut off the car and restarted. Back to normal. Talked to Subaru and of course they had no idea. At least I know I'm not the only one but it hasen't happened since. That was @ 1400 miles, I now have 2800.

[Euclid]

If you parked the other way you would have had more gas in the tank !!!

 

Seriously though, it's the fuel guage in the tank. It's probably more towards the front of the tank so if you park facing up hill. It will read a bit lower.

[Driver72]

Is this your first car?

 

EVERY car's gas gauge reads differently on inclines.

The float mechanism on some cars are located in different spots of the

tank. Therefore, if on an incline the gas won't be level in the tank and therefore

you won't get an accurate reading.

 

And so you know, I don't know of ANY vehicle whose markings on the gas gauge

are perfectly accurate and uniform throughout the tank of gas.

You'd think that if you had a 16 gallon tank, that every 4 gallons the needle would

drop 1/4 of the way down.

Not so. Usually the top of the tank is larger (wider) and the bottom smaller (skinner)

so the needle will stay at the top half longer and then drop much quicker once you

get to 1/2 tank.

Again, it's been that way on basically every car since the invention of gas gauges.

Nothing new.

[dustinw]

Is this your first car?

 

EVERY car's gas gauge reads differently on inclines.

The float mechanism on some cars are located in different spots of the

tank. Therefore, if on an incline the gas won't be level in the tank and therefore

you won't get an accurate reading.

 

And so you know, I don't know of ANY vehicle whose markings on the gas gauge

are perfectly accurate and uniform throughout the tank of gas.

You'd think that if you had a 16 gallon tank, that every 4 gallons the needle would

drop 1/4 of the way down.

Not so. Usually the top of the tank is larger (wider) and the bottom smaller (skinner)

so the needle will stay at the top half longer and then drop much quicker once you

get to 1/2 tank.

Again, it's been that way on basically every car since the invention of gas gauges.

Nothing new.

 

+1 One of the first order of business in a new to you car, is fill up the gas tank, reset the trip meter, and see how far you go on a tank. Paying attention to the gauge during the interim.

[RODMAN]

Actually that's not quite what happened to me. I started my car and it read full. Then I turned it off because I forgot something in the house. When I restarted it it read 3/4 tank. Then I turned it off restarted and noticed it was full again. I still own a Maxima and It has never happened in the 5 years I've owned and the 2 years at this house.

[Sneezy]

My Saab used to do that except it would read empty when it was full. Just one of the many reasons they bought it back. Keep an eye on it.

[unobtainium]

Speaking of fuel mileage, anyone know how the "Average MPG" number is calculated? I notice that the range estimate will go -up- once you get onto the freeway, and I have to believe the machine thinks it knows remaining fuel, the amount delivered and the distance covered. They might be boxcar averaging and they might be integrating, but I wonder how they weight the calculation and how long the effect of a maximum throttle blast shows up in the displayed reading.

 

I called up SOA just to see if they knew, and they did not. There's some EE in the Fuji works who figured out the algorithm, but it sure isn't discussed in the manual or anywhere SOA can find.

 

FWIW mine was indicating 23.7 this morning and it seems close to the right number based on a fill-up.

[Driver72]

It most likely calculates the "average" based on

engine speed, road speed, and throttle position.

If the ECU reads all three of those things, and based on

programmed fuel economy mathmatics, the ECU

can give an "average" or "current".

 

You'll find those MPG computers are rarely perfectly accurate,

and BY FAR more often than not optimistic.

Usually doing the math at fill up reveals you got worse than

what the MPG computer states.

 

That's pretty true for ALL cars.

However, my 05 Grand Caravan has been the most accurate

so far.

On a 420 mile trip, it read 23.9 MPG. At fill up and doing the math

I got 23.7 MPG.

On a tank full in just city driving it said 20.1 at fill up it was 19.4 mpg.

 

My Maxima is almost always off by 2.0-2.5 MPG

My Corolla was about 1.5 MPG off consistently

and so far my LGT seems to be off by about 1.0 MPG