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

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.

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

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!

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.

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.

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

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.

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

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

dag

Originally posted by hotpot
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.

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?

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

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.

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.

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

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.

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

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

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

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!

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?

Originally posted by 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

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?

Originally posted by 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?

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 (http://www.canadiandriver.com/articles/jk/at_000626.htm) which describes the evaporative emissions control systems:Evaporative emissions come from the fuels, oils, rubber, and plastic parts used on our automobiles. Most of the emissions come from the fuel and this has been controlled using a charcoal canister connected to the vent line from the fuel tank. The charcoal canister is filled with activated charcoal (carbon) that attracts the hydrocarbon fumes evaporating from the fuel just as bees are attracted to honey. Each gram of activated charcoal can hold up to 1000 times it's weight in hydrocarbon fumes.

The magic of the canister is that it can release the fumes when fresh air is pulled through the charcoal, so the canister can be used over and over again. Air is pulled through the canister by engine intake manifold vacuum and the hydrocarbon fumes are burned inside the engine instead of being released to the atmosphere.

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

Originally posted by Gord96BRG
IIf 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!

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

This AAA article (http://www.ouraaa.com/traveler/0205/use_b.html) , which says: Finally, do not overfill the gas tank. Stop filling the tank when the nozzle clicks off. If you don’t stop, you could damage the solenoids, valves, sensors and evaporative canister–a costly repair.

Also, a general warning here (http://www.nwicc.cc.ia.us/Module5.htm) : Do not overfill the gas tank. After the nozzle clicks off, add just enough fuel to round up to the next dime. This will prevent damage to the vehicle's fuel evaporative system.

and a discussion thread
here (http://www.cartrackers.com/Forums/live/Toyota/202.html) 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

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.

Originally posted by 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

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...

Originally posted by Squidward
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...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.)

Originally posted by 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. 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...

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.

Originally posted by 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...

ummm. what do you mean by "work really hard"?

heh.. I didn't have to work at all.. just did the usual thing everyone does when pumping.. what happened was either the nozzle was faulty or I didn't have it all the way in (I sometimes do this to get more fuel into the car). Anyway, it overflowed on its own, as the nozzle failed to stop automatically, as it normally does. Fuel gushed out and poured down the side of my car (was an aweful site). Nonetheless, no problems resulted other than leaving a big smelly mess behind.

Its Sunday and I'm relaxing with a 6pack of Sam Adams. So pardon me while I blather...

After reading this thread I had a flashback of the time I took apart a jetski fuel tank and found the fuel level sensor...

I don't know about the RX-8 in particular, but I think fuel level sensors might be linear rods with several concentric floats along its length. If all the floats are in the upper limit, then the tank is full. If half are in the upper limit, then the tank is half full. If all the floats are down, then the tank is empty.

Now look at the attached picture.
What if the shape of the fuel tank itself was not perfectly cubic? Then at the beginning of the tank more volume of fuel would be used to mark a "half used" tank, and the later half would actually be a lower volume.

So really, the fuel gauge that shows a reading of "half" might be reporting that your fuel level is "halfway down the tank" and not necessarily "halfway through the entire volume of the tank"...


This make any sense? Thats my story and I'm sticking with it...

:cool:

Originally posted by 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!


Not to mention the gases need room to expand, when you top off the gases don't have any room to expand, and with your gas cap on it can create a highly combustable situation.

I have always topped off the tank in every car that I've owned and have never had any related problems. I do it to have a consistent bechmark to gauge how much fuel I've used. Different pumps have very different automatic cut-off sensitivity and you're not always sure you have the same amount of fuel in the car when it is triggered. I have gotten in anywhere from 1/4-3/4 gallons in after the auto-shutoff. I had my Probe callibrated to where I could tell within probably 5-10 miles of when it would run out of fuel and always knew how much gas it would take on a fill up. I'm still trying to get a feel for the 8 - I overflowed the very first fill-up because it only took 13.9 gallons and I expected it to take much more!

It would make sense for the tube to the evaporative emissions sytem to be located at the top of the filler tube, thereby making is difficult for liquid gas to get in there. Pressure build-up shouldn't be a problem because vapors (being gases) will always find their way out of the evaporative emisison system. Also, if topping off was such a big problem, wouldn't ordinary sloshing from spirited driving be as much of a concern?

at the mobile gas station near my place, I typically pump at least a gallon after the auto shutoff. no problems encountered.

how many clicks do you allow when closing the filler cap? I used to do three clicks on my honda and do the same on 8 though the manual says "To close the filler cap, turn it clockwise until it clicks".

The "Car Talk" brothers agree:

Don't Top Off Your Gas Tank

When you're refueling, stop when the gas pump automatically turns off. Why? Besides the embarrassing stain on your chinos, overfilling your tank can ruin your gasoline-vapor recovery equipment. The recovery canister is supposed to store gasoline vapors rather than release them into the atmosphere. But if you overfill the tank and liquid gas sloshes into the canister, it will stop working, contributing to the formation of ground-level ozone, smog, acid rain, and airborne toxins.

Hey GIN, I see your point on the sensor of the tank to a point. I know in most marine vessels they use a very simple non-electric slider rod to gauge gas in the tank. That's why in most boats when you run in choppy water the gas guage bounces all over creation. The biggest reason for using that system is for simplicity. If they used an electric sender in the tank for a boat or jet ski, it will more than likely fail simply due to the fact that you are exposing the whole vehicle to water all the time. Water and electronics don't mix. Most gas sensors in cars are electronic for the opposite reason. If a car company put a simple slider rod in a gas tank, every time you hit a bump, it would read all over the place and people would freak. I agree with you though that most senders just show you that you have used the upper half of the tank not necessairly half of the total volume of the tank.

Originally posted by Maximus
how many clicks do you allow when closing the filler cap? I used to do three clicks on my honda and do the same on 8 though the manual says "To close the filler cap, turn it clockwise until it clicks".

I turn it until it clicks a few times,
then I lean into it hard and close it very tightly...

I've noticed a couple of times in the past that if I just relied on the clicks, the next time I refueled, the cap would come off VERY easily. A bit alarming, so now I make an extra effort to tighten it each time.

Don't want that CEL/MIL occuring!

Topping off too much may cause the fuel gauge to not properly showing fuel level for a while (i.e not showing F after you topped off) and only works again properly after you consumed enough fuel there after.