Gasoline Tips Save Money: true?

So this one is going around Facebook. I wanted to run it past my trusted scientifically literate friends here at PF before heeding any of the "advice."

TIPS ON PUMPING GAS
I don't know what you guys are paying for gasoline.... but here in California we are paying up to $3.75 to$4.10 per gallon. My line of work is in petroleum for about 31 years now, so here are some tricks to get more of your money's worth for every gallon:
Here at the Kinder Morgan Pipeline where I work in San Jose , CA we deliver about 4 million gallons in a 24-hour period thru the pipeline.. One day is diesel the next day is jet fuel, and gasoline, regular and premium grades. We have 34-storage tanks here with a total capacity of 16,800,000 gallons.
Only buy or fill up your car or truck in the early morning when the ground temperature is still cold. Remember that all service stations have their storage tanks buried below ground. The colder the ground the more dense the gasoline, when it gets warmer gasoline expands, so buying in the afternoon or in the evening....your gallon is not exactly a gallon. In the petroleum business, the specific gravity and the temperature of the gasoline, diesel and jet fuel, ethanol and other petroleum products plays an important role.
A 1-degree rise in temperature is a big deal for this business. But the service stations do not have temperature compensation at the pumps.
When you're filling up do not squeeze the trigger of the nozzle to a fast mode If you look you will see that the trigger has three (3) stages: low, middle, and high. You should be pumping on low mode, thereby minimizing the vapors that are created while you are pumping. All hoses at the pump have a vapor return. If you are pumping on the fast rate, some of the liquid that goes to your tank becomes vapor. Those vapors are being sucked up and back into the underground storage tank so you're getting less worth for your money.
One of the most important tips is to fill up when your gas tank is HALF FULL. The reason for this is the more gas you have in your tank the less air occupying its empty space. Gasoline evaporates faster than you can imagine. Gasoline storage tanks have an internal floating roof. This roof serves as zero clearance between the gas and the atmosphere, so it minimizes the evaporation. Unlike service stations, here where I work, every truck that we load is temperature compensated so that every gallon is actually the exact amount.
Another reminder, if there is a gasoline truck pumping into the storage tanks when you stop to buy gas, DO NOT fill up; most likely the gasoline is being stirred up as the gas is being delivered, and you might pick up some of the dirt that normally settles on the bottom.
To have an impact, we need to reach literally millions of gas buyers. It's really simple to do.

Sounds reasonable.
But what worries me the most is how accurate the machines are when tallying up the amount you owe. How much of the gas I pay for is getting left in the hose? Or getting returned back to the reservoir? It seems like sometimes the money counter is going but no gas is coming out yet. I don't trust those machines.

Before I used to pay with a debit card, my favorite thing to do was to see if I could squeeze out that last fractionally priced bit of gas without going over what I was paying. i.e. I would get to 10 dollars, and then give it that last little micro-pump that didn't quite cost another cent.

I always wondered how much gasoline we waste as we take the nozzle out of the tank. There is always some drip. Overtime it must be a huge amount. A no drip nozzle shouldn't be so hard to make.

D H
Staff Emeritus
Well Snopes has a discussion on it saying some parts are true and some are under dispute:

http://www.snopes.com/inboxer/household/gastips.asp
I read that as Snopes calling every single one of those so-called savings tips into question.

The only rule I try to follow is the half-tank rule, and it has nothing to do with saving a few cents. It has to do with getting the blank out of Dodge, ASAP. A quarter of a tank will not suffice when natural disaster strikes and you need to get out of Dodge, ASAP. You can't buy gas because the gas stations will either be closed or out of gas. A quarter of a tank will get you halfway out of Dodge because the freeways will be jammed, resulting in the worst gas mileage ever.

I live where hurricanes strike, so I try to keep my tanks half full during hurricane season. For others, well, there are floods, forest fires, and of course zombie attacks. Ya never know when the next zombie apocalypse will strike.

Drakkith
Staff Emeritus
I don't worry about saving 5ish cents per tank. I just fill up whenever I need gas.

ah, good old snopes. See, I trust the people on this forum so much I check here first.

Well, overall it's not a big deal for me. I bike-commute to school and my wife has a 6 mile commute to work. We spend \$30 a month on gas. But I was wondering about the science, or lack thereof, in the article.

I bought 25l of 95e for 1.279euro/l today and paid 32euro for it. So yes, I lost 2.5 cents over 25l..a major calamity.
Additionally I filled a 10l canister for which I paid 12 80 and it was perhaps half a shotglass shy of 10l.

Must be an American thing then

russ_watters
Mentor
If the air takes all night to cool, how much do you really think a 1000 gal underground tank takes? Please provide your answer in months...

collinsmark
Homework Helper
Gold Member
Working

[Source: http://xkcd.com/951/]

With mouse-over: "And if you drive a typical car more than a mile out of your way for each penny you save on the per-gallon price, it doesn't matter how worthless your time is to you--the gas to get you there and back costs more than you save."

D H
Staff Emeritus
With mouse-over: "And if you drive a typical car more than a mile out of your way for each penny you save on the per-gallon price, it doesn't matter how worthless your time is to you--the gas to get you there and back costs more than you save."
That xkcd comic misses one thing: What if I blow out my car's fuel pump?

Hurricane season is well past its peak, almost nothing to speak of so far. In a month or so I'll relax my "keep the gas tank at least half full" rule to my off-season "keep the gas tank at least a quarter full".

From the perspective of a point of view that looks only at the time cost of money of filling a gas tank, it's best to drive the car until it is just short of empty and then fill it to the brim. While this minimizes the number of trips to the gas station, it increases the probability one will need to call a tow truck and have the car hauled to ones favorite mechanic. That last quarter tank is very hard on a car. That's where all the sludge settles, and even if the tank is sludge-free, pumping that last quarter tank out of the tank is hard on the fuel pump.

AlephZero
Homework Helper
If the air takes all night to cool, how much do you really think a 1000 gal underground tank takes? Please provide your answer in months...

Yeah, but the tips came from California. With all the high tech stuff they do in Silicon Valley, it stands to reason everything happens quicker over there

At least in the UK, the price differentials between different gas stations are pretty stable over time, so the simplest cost saving is just avoid the ripoffs. The cheapest pump prices are usually the supermarkets, with further discounts off the pump price for their store credit cards etc, and most people visit them regularly anyway so there's no extra mileage involved.

The places to absolutely avoid in the UK are motorway service areas, unless you are spending somebody else's money with a company credit card!

Drakkith
Staff Emeritus
That last quarter tank is very hard on a car. That's where all the sludge settles, and even if the tank is sludge-free, pumping that last quarter tank out of the tank is hard on the fuel pump.

Both of these things sound like a myth.
For one, I don't think sludge builds up in your tank in this way.
Second, how is the last quarter tank any harder on the pump than the first three-quarters?

I've been an automotive mechanic for 10 years, and the tiny amount of sludge and water at the bottom if the tank is not worth worrying about, however, the gas is used as a cooling medium for the fuel pump, and going below 1/8-1/4 tank can cause the pump to overheat. Doing this repeatedly will cause the pump to fail. Trust me, I've made quite a few pay checks replacing pumps after someone ran low/out of gas.

Drakkith
Staff Emeritus
I've been an automotive mechanic for 10 years, and the tiny amount of sludge and water at the bottom if the tank is not worth worrying about, however, the gas is used as a cooling medium for the fuel pump, and going below 1/8-1/4 tank can cause the pump to overheat. Doing this repeatedly will cause the pump to fail. Trust me, I've made quite a few pay checks replacing pumps after someone ran low/out of gas.

I'm assuming that everything's okay until you actually run out of gas? Even if it's just low, you still have fuel doing its thing in the pump?

I'm assuming that everything's okay until you actually run out of gas? Even if it's just low, you still have fuel doing its thing in the pump?

To an extent...

The fuel pump is usually about 3/4 the height of the tank, so at 1/4 tank about 2/3 of the pump is exposed to air, with only the lower most portion being properly cooled (i.e. Keeping the temperature below 150 degrees F).

When the gas level is low, the electric part of the pump warms up quite a bit and can burn out the coils. Actually running out does damage to the mechanical parts of the pump because the gas is needed to lubricate the gears, impeller, etc. and if you run out then you no longer have that lubrication, thus the internal components start grinding themselves apart.

As this image shows, the electric motor in the fuel pump (which is the most vulnerable to overheating) is also the highest part of the pump, so it looses cooling first in a low fuel situation.

russ_watters
Mentor
I've been an automotive mechanic for 10 years, and the tiny amount of sludge and water at the bottom if the tank is not worth worrying about....
Which I avoid completely by draining the tank every time, thus preventing either from building-up.
....however, the gas is used as a cooling medium for the fuel pump, and going below 1/8-1/4 tank can cause the pump to overheat. Doing this repeatedly will cause the pump to fail. Trust me, I've made quite a few pay checks replacing pumps after someone ran low/out of gas.
Low is not out. This sounds like another myth. Unless the gas is circulated through the tank to cool the pump, the tank level can't affect the cooling capacity of the gas.
The fuel pump is usually about 3/4 the height of the tank, so at 1/4 tank about 2/3 of the pump is exposed to air, with only the lower most portion being properly cooled (i.e. Keeping the temperature below 150 degrees F).
Wait, what? Are you saying the fuel pump is inside the fuel tank?

OmCheeto
Gold Member
Which I avoid completely by draining the tank every time, thus preventing either from building-up.

Low is not out. This sounds like another myth. Unless the gas is circulated through the tank to cool the pump, the tank level can't affect the cooling capacity of the gas.
Wait, what? Are you saying the fuel pump is inside the fuel tank?

Mine was. And that's why I pulled my external fuel pump, from car minus 4, hooked it up to my boats 6 gallon portable gas tank, and drove car minus one, to the Red-Green automotive shop about 12 blocks away.

They were so impressed, they replaced my in-tank fuel pump, for cost.

I really need to find those two guys, and thank them.

Low is not out. This sounds like another myth. Unless the gas is circulated through the tank to cool the pump, the tank level can't affect the cooling capacity of the gas.
Wait, what? Are you saying the fuel pump is inside the fuel tank?

Yes, On a fuel injected engine the pump is located inside the tank and gas is cycled through the tank to cool the pump. It goes in through a port on the top of the tank and the bottom of the pump rests on, or very close to, the bottom of the tank.

OmCheeto
Gold Member
Yes, On a fuel injected engine the pump is located inside the tank and gas is cycled through the tank to cool the pump. It goes in through a port on the top of the tank and the bottom of the pump rests on, or very close to, the bottom of the tank.

I should probably add a warning about my clever way of getting my car to the repair shop.

My 6 gallon portable fuel tank was about half full when I started. When I got to the shop, it was nearly empty. I'd driven less than a mile in under 5 minutes. I asked the mechanics about this and they said the gas had been pumped to the fuel injector rack, and any excess gas was ported back to the main fuel tank. I assume this assists in the cooling process.

Had my main fuel tank been nearly full when I started the trip, I would have overfilled it, and would have had a major gasoline spill.

Sometimes, being clever, can have its drawbacks.

Next time, I'll call a tow truck.

This has been a great discussion. Though I don't know if I feel more or less informed about the issue at hand. I'll probably keep taking my bike.