Rotary Titus

In the 8, I noticed that the low fuel warning light comes on even before the needle hits the bottom of the guage (where as all the cars I've seen only turns on the light at or after the "min" mark and the needle goes "below the scale" while running on reserve) so does this mean on the 8, what the guage says is the absolute fuel that's left in the tank, INCLUDING reserve?? thanks

Zeltar

Yes. Think of it as a true guage. It doesn't stay on Full for long. And, when it hits empty, it really is empty.

Rotary Titus

cool thanks
wow good thing I didn't keep going thinking the needle could go below the scale!

Kagero

I have filled up when the neddle was below the "E" and still was only able to get 13.56 gals in tank. I pushed the handle at least
3 times easy too! I have never got lover then 19.5 mpg. At best
23.5 mpg. I'm happy with entire car!

Haze

You filled it below E? Wow, not mine. E is E for empty on my car, but all gauges run a little differently in different cars. With two ticks left on the meter, and the light firmly on, I pump in about fourteen gallons. I'm not going any lower than that.

hotpot

The fuel gauge sucks.
Last night when I switched off the car, the needle was exactly on the 1/4 mark. This morning when I started the car it was one tick above the 1/4 mark.

After a fill-up the needle shows about 2 ticks above the F mark. When it hits the F mark, I will have covered 30 miles.
By the time it hits the 1/2 mark, mileage is about 125 miles. So it's about 95 miles from F to 1/2.
By the 1/4 mark mileage is 195 miles, i.e. 1/2 to 1/4 mark = 70 miles.

As you can see the gauge is very erratic and not linear at all. I would fill up as soon as the light comes on as the gauge is not to be trusted.

Shooter

I got 14.1 into the tank on sunday when i filled up after running with the light on for probably 10 miles.(no station close by). Still getting around 16 mpg but my commute to work is 3.5 miles each way so I don't expect to get good mileage anyway.

RX8Z

Guys, wuteva you do.. DONT TOP OFF YOUR GAS !!!

dag

RX8Z - OK I'll bite - why shouldn't we top off the fuel?

dag

Squidward

you figured that out, too?

I've put alot of focus to keep track of the fuel consumption to attain running average mpg, however soon learned how erratic the needle is. One moment, I think I'm getting 60 miles every quarter tank, then the next moment, the needle takes a dive into the next quarter tank in the next 10 miles... the fuel gauge sensor in the tank must have been designed poorly...

I wonder if its a mechanical sensor or electronic one.. anyone know?

Shooter

I didnt do anything different when i filled up and got 14.1 gallons in the tank. I fill it until the pump clicks off by itself. I dont force anymore into the tank.......

Topping it off doesn't matter anyway, does it? I don't see what effect that would have on the car.

FirstSpin

I can't imagine topping off the car hurting anything. Not sure why that was dropped on us from out of the blue.

Regarding the yellow light. I got caught asleep at the switch one morning and the yellow low-fuel light came on. I've posted this before and I'm going from memory now so hopefully the two posts will agree reasonably. I drove about 8 to 10 miles past the point where the light turned on. The car held 13.something, I think 13.6 gallons. Someone else on here said that they ran out once and our 15.9 gallon tanks only take 15.2 when dead empty (must be a heel in them somewhere). Based on all of the above and my normal mpg of 15 to 17, I figured I had about 30 miles max that I could have safely driven after the light first came on.

Not really an issue with me normally, since I am fairly conscientious about filling the tank when it gets to about 1/4 full.

allstate

My experience with topping off the 8 was that just a few more clicks on the handle caused the tank to overflow. In other words when the pump turns off...the tank is full. I no longer attempt to add any more fuel after it shuts off.

Gord96BRG

It sure does matter! It won't have any direct effect upon the engine running, but the filler neck incorporates a vapour capture system - it's part of the evaporative emissions control system. If you overfill the gas tank to the point where fuel is up in the filler neck, you can flood the charcoal canister with raw gasoline and ruin it. If the vapour capture system isn't working properly (ie as a result of being flooded), I believe you can trigger a CEL. On any modern car, never fill beyond the auto-shutoff!

Regards,
Gordon

Rotary Titus

wow, thanks
who knew topping off could do that?!

rx8gator

I don't top off either because I noticed you cannot get that much more in anyway, and usually end up overflowing (ruining my nice Zaino!). I did not know that there was a sensor there for emmisions. A bit of common sense helps here!

mcballz13

Getting back to the mileage thing... I keep track of every tank through my mileage... I do a lot of driving and find myself on "E" at least twice a week so of course I wait till the last calulated second to fill up. My light comes on well before the needle actually gets near the Empty line and I have gone past the line as well... I agree the needle and guage are a little screwy, however I have gone up to 30 miles with my gas light on and have still only put in 14.2 gallons at most! So maybe everyone's tanks do vary greatly?

hotpot

Excuse my ignorance. But what is a charcoal cannister, where is it and what does it do?

I usually fill up the the max to get maximum mileage out of a tank. I don't like going to gas stations.
Is there a warning in the manual about not filling up to the top?

Gord96BRG

I just checked - there's no warning in the RX-8 manual about filling beyond the auto shut-off, but there is in the owners manuals of many other cars.

I found one article here which describes the evaporative emissions control systems:If the canister becomes flooded with liquid fuel, it can be ruined. I don't have time right now to search, but there should be plenty of other articles in the wonderful internet world that describe this! Offhand, I do not know where the evaporative control canister on an RX-8 is located.

Regards,
Gordon

Gord96BRG

Lunchtime! I had time for a quick search, and found two references to the dangers of overfilling beyond the auto-shutoff:

This AAA article , which says: Also, a general warning here : and a discussion thread
here where Toyota Corolla owners discuss problems where fuel filler vent issues can make their cars prone to destroying the charcoal canisters if overfilled (possibly subject to a recall?).

Hope that helps,
Gordon

hotpot

Thanks for the info Gordon. I was just wondering if this is such an issue, why they don't mention anything about it in the manual. Or is it common knowledge? I've always filled up all my cars to the brim and was never aware of this issue. The gas station attendants don't seem to be aware of this neither since they also fill until no more gas can go in.

Squidward

I'm not so sure about that.. I had a 2001 AUDI TT which I topped off all the time without problems.. And one time, the nozzle shutoff failed and overflowed the tank (gas pouring down the side of my TT). I put the cap back on and started the engine and everything was ok.

I guess there are exceptions...

BillK

Most modern gas gauges are not designed to be linear at all. In fact, they are designed to be much more sensitive in the lower ½ tank as compared to the top ½ (because automakers believe, and rightly so, that accuracy is more important when the fuel gauge is reading in the bottom half of the tank.)

BillK

You actually have to work really hard to get gas into the charcoal canister on most vehicles.

When gas overflows while filling the tank or topping off it's almost always due to air within the tank forcing the fuel back out. You have to work pretty hard to get all the air out to the point that fuel actually backs up within the evap system...

stormchase13

I used to fill my Camaro to the brim every time and never had any problems. The 8 is a different story though...filling-wise anyway. It doesn't matter if the gauge is just below the 1/4 mark or a hair above "E", I'm hard-pressed to get any more than 13.5 gal. or so into the tank. It seems to me that the configuration of the fill pipe and tanks might 1) trap a lot of air in the tank and/or 2) doesn't allow the gas, even at slow rates, to flow properly which causes a backup and trips the pump sensor.