Buying gas the right way

[sunfire]

I just saw this at the AAP site, on the main page (creative ways to save more gas). Is this fact or fiction?

Buy gasoline during the coolest time of day—early morning or late evening is best. During these times gasoline is densest. Keep in mind that gas pumps measure volumes of gasoline, not densities of fuel concentration. You are charged according to volume of measurement.

I just buy gas when the light comes on mostly during the day. The gas tanks are usually underground, does it make a difference?

 

[mpvue]

http://www.snopes.com/inboxer/household/gastips.asp

 

[Pablo]

There was a thread about this awhile ago. I forgot who won.

I say it doesn't matter, or the difference is tiny. Yes if you live a hot place you will lose more gas from evaporation, but the underground temperature of the fuel doesn't fluctuate that much plus it's a liquid.

 

[sunfire]

I'm going to give it a try. The whole gasoline evaporation theory makes sense. I’ve seen people recommending that the gasket in the gas cap should be replaced. My Corolla’s engine light came on once because I forgot to click the gas cap.

It might make more of a difference since I am starting to see 70 degree days. I always jot down the travel mileage after every fill. I am really curious, if this really makes a difference.

 

[NYSteve]

I actually made replacing the gas cap part of my initial round maintenance when I buy a used car(along with fluids, filters, plugs, etc). Had a car, with the gas filler in the back not side, where I once parked it on an incline and started seeing gas coming out with the cap fully tightened. Replaced and no more problems. But how long would it take you to run down a bad gas cap once you start throwing codes, mpg decrease, etc? Just too easy to replace it every few years and avoid the headache.

 

[Quest]

+1 to Pablo's comment.

It's just 1 of those urban legends that simply won't go away, and conspiracy theorists just snap these up on the internet like hotcakes....

Q.

 

[Shannow]

Only time that you will get any sort of reasonable variance is directly after a tanker drop in a hot climate like Oz, where the fuel takes 4 hours in the sun to reach the station.

Other than that, the ground here is a nice stable 15 degrees (give or take).

 

[Gary Allan]

Wait until stations start selling fuel with temperature compensation tables built into the pump. You'll see $5.29/standard gallon on the sign..but the pump may read $5.38/temperature compensated.

 

[Cutehumor]

I would think making sure your gas cap is tight makes more of a difference than anything. gasoline is lost that way.

 

[chief]

I dont think it may a lot of difference. Im in the trucking business and there was a lot of chatter about hot fuel and how much it can hurt you bottom line. I carried a clean quart jar and a thermometer with me and started filling the jar and checking the temp while I was fueling. It varies very little if any at all as to the time of day or night. Of course it going to be cooler in winter and warmer in the summer time but the time of day is mute. Most of these storage tanks are in the ground deep enough the surrounding soil is about a constant temp given the season of the year. This of course was diesel fuel and nor gasoline which will evaporate at a greater rate than diesel.

 

[Mr Nice]

Worry more about the PSI of air in your tires than the temperature of the gasoline.

 

[Saturn_Fan]

All my cars have locking gas caps I install as a standard item when I purchase them.

 

[Audi Junkie]

Bzzt.

 

[Lorenzo]

I don't know about the best time of day to buy gas, but when you see cars dropping like flies as they drive away from the station, there's a clue you should go somewhere else ...
http://www.courierpostonline.com/apps/pbcs.dll/article?AID=/20080418/NEWS01/80418013

 

[crinkles]

Originally Posted By: Lorenzo
I don't know about the best time of day to buy gas, but when you see cars dropping like flies as they drive away from the station, there's a clue you should go somewhere else ...
http://www.courierpostonline.com/apps/pbcs.dll/article?AID=/20080418/NEWS01/80418013


"Water can cause a car to stall because it is heavier than gas."

by that rule our cars should run GREAT on air, because it is lighter than gas!

I think the problem here is that water doesn't combust but I'm no chemist

 

[Benzadmiral]

"Fill up at the cooler times of day"?

In The Swamp there IS no cooler time of day. . . .

 

[INDYMAC]

The fuel density/volume/temperature vs. $ problem isn't that significant in an automobile with small tanks (13-26 gallon tanks), but you can make money if you routinely fill up during the coolest part of the day. Your tank will be cooler and allow for more volume of gas too. But, it's probably not a good idea to let that full tank sit for the remainder of the day while it starts to expand.

While flight planning in the Navy, fuel density was a critical variable that we used for take-off weights, cruise altitudes, various ranges we could fly, and what alternate airfields we could use if there was a problem at our final destination.

Here is a quote from an old P-3C NATOPS manual on fuel density vs. temperature:

For accurate mission planning, the combined effect of initial fuel density and temperature must be considered for the fuel onboard. Assuming the fuel being used has an initial fuel density of 6.3 pounds per US gallon at 15C/58F (standard day), the same fuel at a temperature of 40C has a density of 6.15 pounds/gal. For an aircraft with 9,200 gallons of fuel, the load would be 56,580 pounds as compared with 58,510 pounds for nominal JP-4 at the same temperature. (JP-4 is the least dense with the lowest flashpoint of the military jet fuels. JP-5 and JP-8 are the others. JP-5 has the highest flashpoint/highest density/lowest BTU's of the 3 and is used for shipboard ops).

This extra 2,000 pounds of fuel would give me an extra 30 minutes of flight time if I needed it. That's why I always preferred early morning pre-flights for long missions. My experience with flight planning shows the OAT vs. density conversion table we used was fairly accurate. I think the ambient temperature of the aircraft fuel tanks and the already existing ramp load warmed up the incoming fuel very rapidly.

The density vs. temperature ratio is linear for all 3 JP's, so I would expect gasoline and diesel fuel to be of similar weights and ratios.

I hope this adds something to the discussion, or maybe I just found my old NATOPS manual for nastalgia! That's OK too.

 

[[RT] ProjUltraZ]

that's interesting, i guess the aircraft fuel gauge is translating fuel volume to pounds of fuel as there is no mass increase w/ temp.

it's showing a 3.4% increase in volume going from 58 F to 104 F, and JP is similar to a diesel fuel

 

[SecondMonkey]

Gasoline is stored in GIANT underground tanks. Ground temperatures are constant throughout the day and throughout the year. Gas does not change temp, day or night, january or august.

 

[INDYMAC]

Yes, fuel quantity gauges measure total pounds and fuel flow gauges are in pounds/hour. We considered FF gauges to be one of the most accurate gauges on the aircraft.

Fueling was done via fuel truck from large (huge) above ground tanks, or from "hot fuel pits" with below ground tanks (a tactical aircraft favorite). Shipboard fueling is obviously quite different, but didn't apply for a P-3 anyways since it was land based.