Squidward

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.

GiN

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...

Astor

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.

DemonRX-8

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?

Squidward

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

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".

New Yorker

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.

vmiller6

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.

Squidward

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!

yiksing

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.