Stavesacre21

Has anyone noticed a certain "tier" that the fuel guage will eventually stick on for an inaccurate amount of time?

After 11K miles on my 8, i've noticed this again and again and again. It's always VERY prevalent on highways. I'll usually get about 120 miles or so on the first half of the tank, and then EVERY TIME, it will drop to the 2nd hash mark below half tank, and will sit there for about 40-60 miles...and doesn't move at ALL. Sometimes it makes it a little hard to estimate how many miles you've got to go.

I figured that maybe it has something to do with the shape of the fuel tank and how the amount is measured, but was curious as to if anyone else has ever noticed it...kinda hard to miss when on the highway for extended periods of time.

It's not a big thing, but I'd never read previous posts on here about it, and I know that we tend to cover almost every inch of the 8's quarks.

CarAndDriver

I will have to check it out. I am at the 1/2 way point on this current tank.

The fuel gauge is very accurate. When its at the 1/2 way point about 1/2 the tank is gone.

Overall, its drop is too fast for me.

Stavesacre21

Always is too fast!

But yea, every other part of it is fluent up until then...then afterwards it falls at the regular rate again.

CTrx8

iTrader: (2)

funny you should mention that. i noticed that the last few weeks.

RX8KRIS

Mine does the same thing, so I just figure when I get to 240 miles its time to fill up. Don't even look at the gas guage anymore.

MrSuicideDoor

i've definitely noticed the exact same thing. the first 3rd of the tank drops so fast, then from 1/2 to 1/3rd it takes its time. that's why i only fill my car up halfway. lol

CTrx8

iTrader: (2)

240, huh? i'm not complaining since work pays for gas but i'm happy when i break the 100 mile mark at halfway. of course my commute is a nice warming up of the car in the morning and a 3 mile each way stop and go. so not great for any car's gas mileage.

Raptor75

Yes, and it really annoys me. I have also notice that it will change with the seasons or in other words it report differently in hot and cold climates.

Here is what I believe causes this or at least has an effect on it.

Warning, I have no confirmation of this and am going from information past to me by other users on this form.

The RX uses a saddle tank which is basically split in two. I have been told that the car will feed from one side and at preset times pump from the other side into the feeder side. This could explain why the gauge could hang at the middle longer as the tank is refueled and Mazda's voodoo recalculates what the gauge should read.

Now on top of this add in the fact that the exhaust pipe run between the two tanks and will heat the gas which will cause it to expand. I believe this is why you will see sudden drops in the fuel gauge shortly after start up. When you shut down the gas is hot and will show a slightly higher amount in the tank, when you start the car the gauge initially show the higher amount but after driving a bit drops a tick very quickly. The weather will also effect this because the tank will keep cool in winter so it will expand less, In summer the opposite.

I have also noticed that almost each time my car has had a new flash from Mazda the fuel gauge will read slightly different. It was very noticeable after the engine recall flash.

Again take this for what it is worth but the end result is a very none linear fuel reading.

mysql101

I get 45-50 miles per quarter tank, it seems very accurate.

Rhawb

Mine hangs at full and then again 1-2 notches above half. Doesn't really bother me, I just know when it's hanging just above half, I'm going to need gas in the next day or two.

04RX8man

Yeah I noticed that too I get about exactly 100 miles out of a half tank and 47 to a quarter tank. 2 lines below half it sits for quite a while then it drops like two then the next day its time to fill up AGAIN! Definatley drops too quickly for me but not much we can do. I just filled up last night and calculated I got 16mpg. Not too good but I ran it hard a few times and it has been snowing so spinning eats gas. haha

Raptor75

Don't feel so bad my last calculation was almost 12 mpg.

Stavesacre21

ok, well im glad to see that i'm not all alone on this whole hash mark thing...I was a lil worried at first.

and as far as I want this to be from a MPG thread, others have mentioend theirs so I may as well toss mine in. At the latter half of my "stuck guage" i always used to get all excited and figure that i could go roughly 320 miles in accordance to how far i'd went at the time. It does however drop more then steadily after the "stuck hash".

Raptor seems onto the pattern though...that emissions reflash was detrimental to not only MPG, but the way the gauge reads too. First quarter is almost 70, then second is usually about 60, then 50, then 40ish. Averaged around 21 combined before, closer to 18.5 now. gauge seems to drop slightly less fluent anymore. I'm thinking that my car always hung around that hash before and after the reflash, but it does seem to act differently. And that saddle tank is one heck of an idea...sounds like a good guess.

CarAndDriver

After this thread, I looked at my gauge and it tends to drop evenly unlike some on this thread.

19.6MPG on this latest tank.