28 August 2008

Unbelievable!

We drove 457 miles on 10.8 gallons of gas. 42 miles per gallon in that Civic! The tank holds 14.2, so we could easily have gone over 500 miles on one tank. Sweet. We also filled the tank on the SLOWEST fuel setting to get less vapor, more gas (tip from Dave!).

15 comments:

Rev. Benjamin Mayes said...

The slow gas thing sounds like an urban legend!

Anonymous said...

Check out snopes.com on the "slow gas" thing.

wmc said...

The speed of pumping has nothing to do with the amount of vapor that is in equilibrium above a liquid. The liquid will displace its volume in vapor as you fill the tank, regardless of the rate. If the liquid is cold, it might actually be an advantage to fill it quickly before the liquid gas warms up in the tank. The amount of vapor present in the empty volume is a function of temperature.

Ah, shades of thermodynamics from another time, another life.

Jeremy Loesch said...

Rev. Weedon, I know nothing about vapor (although I have been accused of being a gasbag). But I do know for certain that Hondas are the best built American made cars. Enjoy your vacation. Jeremy

O.H. Lee said...

I wish I had such awesome gas mileage on my wife's new car. Though it sits in the garage most of the time, we're lookin at 26 MPG on the highway, 18 (or less) in the city. And, it's not even a truck/suv.

I envy your Honda. But, I guess mine is much, much faster! That's all that matters, right?

Dan @ Necessary Roughness said...

wmc:

How fun would it be if gasoline were compressible? :P

Thermal expansion of gasoline in the tank...I'd have to dust off my CRC for that one, but I'm not sure it'd work, considering we use over 20 different blends of gasoline in the United States. Not all "regular" and "unleaded" is the same, as localities require different additives.

Lutheran Lucciola said...

This is true Dan, as I live in the world of "pay to put IN MTBE, pay to take OUT MTBE!"

wmc said...

Thermal expansion of gasoline in the tank...

This actually is a factor, since liquid expands with heating, you are pumping "less" gasoline from a hot storage tank than from a cold one. The retail pumps do not compensate for temperature, though in fact, the difference is not all that great and compensated by a cold tank in the winter.

As for vapor in equilibrium over liquid (pertaining to vapor displacement and pumping rate), additives and the composition of the blend (ethanol) will have an effect on the vapor equilibrium. Still, the rate at which the vapor volume is displaced by liquid does not effect the gasoline content of the vapor when there is no difference in ambient temperature between the storage tank and the car.

Hondas are awesome. Toyotas used to be until they started building them in north America. My current Corolla is falling apart prematurely compared to its predecessor, the indestructible Tercel.

Dan @ Necessary Roughness said...

I misstated what I was saying in my comment.

I meant that I didn't expect to find in my CRC (70th ed. 1989-1990) a table for the thermal expansivity of gasoline, because the formulation isn't standard. There is a table for water, but I wouldn't think water was chemically similar enough to gasoline to draw a similar conclusion.

I understand the concept of liquids reducing in volume as they get colder, except in the case of water where the density starts going back up as the temperature drops below 4 degC.

Yahoo has an interesting discussion on the topic. Basically you save 1% for every 10 degC.

Moral of the story: fill up at night, unless you're in Oklahoma where night is almost as miserable as the daytime. :)

wmc: in your past engineering life, were you a P.E.?

Anonymous said...

I asked my father-in-law how many miles per gallon his 34 Ford hot rod gets. He told me he doesn't measure miles per gallon, but smiles per mile:)

Rosko said...

Dan,
The temperature during the day vs. at night/early morning difference is negligible, given the fact that the gas in the tanks get heated in transit, and sit in an underground tank. The earth around them insulates the tanks, and the temperature effectively only changes as the seasons change.

Rosko

Jeremy Loesch said...

WMC, my first car was a 92 Tercel- 4 speed manual, vinyl seats, no AC, roll down windows, no cup holders. And it was a great car! I drove that thing into the ground. Bought it with 30K miles, sold it for $500 to a pastor friend who needed a car for his daughter. It had over 175K miles on her when I sold it. (Her name was Shannon.) That Tercel was indestructible. Loved driving in snow and passing SUVs in the ditch. Jeremy

Carl Vehse said...

"Ah, shades of thermodynamics from another time, another life."

Rev. Cwirla, if only people would realize a chemist is their friend, especially when the chemist got his training in Kent Hall.

Anonymous said...

"The retail pumps do not compensate for temperature, though in fact, the difference is not all that great and compensated by a cold tank in the winter."

It might, if you have enough "winter"! :)

Meanwhile, filling on a 70 degree morning is supposedly better than filling on a 100 degree afternoon.
(You have to get up early for 70 though.) :(

Helen, in Texas

wmc said...

Kent Hall. Wow! A true blast from the Univ. of Chicago past. I wouldn't recognize the insides of that building today, but those doors say it all. I still remember entering through those doors for freshman chemistry. Great times.