Nathan Plemons

Alright, well we should all know that density, volume, and temperature are related. If we take volume X of say a warm liquid and we cool that liquid down to near freezing our volume will decrease as density increases. Works for gasses too, hence the reason we want a cool air charge. For the same volume we actually get more air.

When I was leaving work yesterday I knew that I needed to get gas. I was down to 2 bars on RESERVE. I could have easily got gas on the way home but made a concious decision not to do so. It was 90 degrees as I was driving home and I knew it would be 50 degrees in the morning. Now I know ground temperature stays fairly constant but it does fluctuate some. I decided to wait until this morning to get gas. My theory was that the gasoline, slightly cooled by the overnight cold temps would give me more gas for my money since the gas pump goes on volume.

It's a pretty sound theory. Even if it's only one or two degrees difference it will be a little bit denser. So how can this get me in trouble? Well unfortunately this theory works for the gas in my car as well. I know this, but apparently I was a little bit lower on fuel than I thought. When I parked my car yesterday afternoon everything was running just fine. I knew it wouldn't be a problem, it's only about a mile to the gas station.

So I get in my car this morning and fire it up. I immediately get the gratifying sound of long tubes through flowmasters, boy do I love that sound. Then it stumbles for a second, falls below the correct idle and then stumbles it's way up. I look over at my fuel pressure gauge which normally reads around 38 at idle, it's bouncing, yes bouncing, around 30.

MY GAS HAD SHRANK!

I thought I might try to limp it to the gas station with a sprint and drift, no love. I got out of my driveway but by then the fuel pressure gauge was bouncing around 15. If I tried to give it any gas at all the car would just stumble and almost die. I knew I had to cut the crap real fast. The fuel pump is lubricated and cooled by the gas in the tank. Obviously it's sucking was sucking air. I limped it back into my driveway where I had to make a decision.

I could drive my dad's truck to school / work today and worry about it later. I'd have the same problem when I got home (unless of course my gas would expand enough) So now regardless of if I was do it before or after work I would have another problem. I don't have an empty gas can. I've got a can with gas for the lawnmower in it. I don't exactly run premium in the Kubota either. The lawnmower is also full, as is my dad's truck. I couldn't just pour this gas out so I could fill it with premium. ARGH!! I knew what I had to do even though it pained me to do it. Grab the funnel and pour some of this 87 octane into the vette. :smash: :smash: :smash: :smash: :smash:

I poured in maybe 3/4 of a gallon and then limped to the gas station. I was expecting the car to be pinging like mad. Luckily it didn't, in fact I never heard it at all. Of course I didn't go banging the car off the rev limiter either. I don't know that I got over 2500 RPM's all the way.

I guess my only saving grace was that there was still some amount of premium in the tank, so when I added the 87 I essentially had mid grade. Remember I said I probably put in about 3/4 a gallon? The gas pump shut off at 18.7 gallons, I went ahead and put in 19.08. Hmm, does that mean I had about 1/4 of a gallon? WAY too close for my taste.

QuikZilver

:eek:
You got lucky!! If I hit reserve, I try to find the closest gas station possible! I had one experience in my Vette that I put in 19.8 gallons of gas. It was just starting to sputter. I lucked out because I had been driving home from work when that happened. :smash:

Red Tornado

:eek: I hear that. I too look forward to hearing the sound of the longtubes with my Magnaflows, as soon as I get them in the next 2 months :thumbs:

C-4 Cross Fire

I hate it when my gas shrinks! :D

I used to put only high octane in my '84 but just decided one day to put in a tank of 87 octane one day and saved a couple thousand dollars (that was 4 years ago!!)!! It runs the same with either one. No pinging. Really. Save a buck or two without even dialing 10-10-220!!

GS-598

Never bet against Physics! Don't always trust fuel gauges.
If the 1/4 gal of gas in the tank was at 90 deg, letting it cool to 50 deg the next day would have reduced its volume. OK, not much, may an injector squirt or two. ( I don't know the coeficient of expansion of gasoline).
Because almost all gasoline tanks are below ground, their temperature stays fairly constantly below the surface temperature so when you fill up, the fuel is typicaly cool.
The expansion with temperature was more noticeble before vapor recovery, rollover valves, etc were installed on cars. Before these things, if you filled up to the top of the neck and let the car sit in the sun, you would have gas running out of the filler.
One last note: the cold fuel being more dense, thus having more "power" per gallon(coils of fuel tubing in canisters ice) was probably more of an issue with carburetors than with todays fuel injection. The electronics can adjust fuel delivery to attain the proper fuel/air ratio, adjusting for both changes in air density and fuel.
BTW, there was, maybe still is a great article on gasoline on the Idaho Corvette web site that explains some of the myths of octane.
Dennis
GS//598

redwing76

Interesting story. "You know just enough to be dangerous".
If your theory was sound it would have followed that you'd have less gas in the morning. Still being lazy is no excuse for running out of fuel.
Here in the PRC running out of gas on a major hiway is illegal.
Still a good story. Mid grade is undetectable in a C-4.

GS-598

In my reply I mentioned an article on gasoline.
Here is the link: http://www.idavette.net/hib/fuel/index.htm
Dennis
GS//598

Southern Comfort

:nonod: interesting theory.

:nopity But you should never have let it get that far down.... :lol:

Steel Blue 91

Yeah, I hate that kind of "shrinkage". Shrinkage of any kind can get embarrassing (especially on a personal level). :jester :jester :jester

jfb

It doesn't make any difference what density your gas was at because the ECM is going to adjust the a/f ratio to be constant so what is important is the mass of gasoline left, not the density! Also, I have found out the hard way to fill the tank as soon as the reserve light comes on or slightly before .

Nathan Plemons

I posted this because I thought it was amusing, not because I needed a lecture on the gas gauge. :rolleyes:

Also, although mid grade or regular might run OK in a stocker I don't care to push it that far. My car is ever so slightly modified and is running a higher static compression ratio than stock. Although I don't know exactly how the cylinder pressures compare to the stocker, I'm willing to bet that with the cam it's a good deal higher than when it rolled off the factory line.

Also keep in mind that just because you can't hear any pinging doesn't mean it's not there and costing you performance. The only true way to figure out what gas my car REALLY needs is to data log it with lower octane fuel and see how much timing if any that it has to pull. So then there's the money issue, which I don't really consider an issue. Since I've owned the car I've pumped 1571.851 gallons of gas through it. So if you consider a $.20 savings per gallon I could have saved $314 over that time. That amount of money wouldn't pay for an engine rebuild caused by severe detonation.

So do I know for a fact that I have to run premium, NO. I do however have the capability to determine that. Whenever I get the time I will do so. In the mean time I'll spend the extra money to be safe. In approx 2.7 years, that's
985 days. $314/985 = $.0031 per day for peace of mind. I can afford that.

Have FUN people. I made a bad call, so what. I can laugh about it, so can you, but theres no point in making it sound like it's the stupidest thing on earth. I guarantee that every one of us has done one worse before.

Nathan Plemons

Not really, it does make a difference. If the gas is a good deal colder you can fit more in the tank. And since the gas pump measures volume rather than mass, you can get more mass for any given volume. You're right, it has nothing to do with the A/F ratio. If the fuel is more dense it will narrow the pulse width, if it's not so dense it may increase the pulse width. Essentially the car needs a certain mass of fuel. Since the volume of my gas tank is constant the only way I can get more gas into the tank is to fill it with gas of a higher density.




[Modified by Nathan Plemons, 11:22 AM 9/18/2003]

Goody

I'm with you Nathan. Except the weird thing is my dash reading said 63 miles till empty (Range reading) which I know is based on current consumption rate. Well, I was sitting at a light, it finally turned green and as I accelerated away the car started to do the sputter sputter on me. :eek: Luckily I found a 7-11 within a few blocks and filled it up. I had 3 bars on the guage then. It did register 2 bars (Reserve) that morning, but moved to 4 bars when I back down to the road.....hmmm, might be a guage issue. I did manage to put a tad over 18 gals into the tank during that fillup though.
My wife is convinced that the car must have gas at 1/4 tank no matter what. I might just have to agree with her for a change about this one. :banghead:

HiRiser

It costs you the same whether the tank is full or empty, so I keep mine full :D

Lichen

That is the wackiest excuse I've ever heard for running out of gas. Had you just finished watching "A Beautiful Mind"?

CentralCoaster

The energy content of the gas is the same, cold or hot.


In fact, I'd guess that when cold, you'd have more usable gas because colder gasoline vapor can't suspend as much moisture (ie liquid gas). So, you'd have more gas in the liquid than in vapor floating around in the tank.

I get fuel chocking problems below 1/4 tank, on hard left turns.
And I always make hard turns!

azzkikr

Interesting story....

I've been told it's never a good idea to run a tank low or dry - because you suck up debris in the bottom of the tank (dirt, rust etc.) which clog filters and lines.

I ran my jet ski dry... (broken gas gauge) Sucked up dirt from bottom of tank and cost big $$$ for carbs to be cleaned.

KY Vette

"Still being lazy is no excuse for running out of fuel."

How about just being stupid? I ran out a few weeks ago, and with a friend in the car! I 'almost' coasted into a station, came up about 50 ft short. My friend was kind enough to push me the last few yards, but I still hear about it!

Doesn't seem to have hurt my fuel pump, but ever since then I've wondered if I damaged it. Probably shortened its life anyway. :cuss

Nathan Plemons

That's about how I feel about it right now, but hey, no harm done. I took a gamble and lost. Oh well, I'll know to get gas on the way home next time.

bogus

hm. All of this abuse... all of that worry... all of that frustration... just to add 1 extra ounce of gas.

wow. seems worth it to me. :rolleyes: