Gas Pump With Money
Home Misleading Gas Saving Tips – Are They Really Saving You Anything?

Gas Saving Tips – Are They Really Saving You Anything?

by Brett M. Christensen

This story was written by David M. White


An email forward that started in 2007 has made the jump to Facebook, added a new bit, and is still as wrong as it ever was. 

Brief Analysis

As fuel prices have increased inexorably over the years, there have been three absolute truths:  Americans are a wee bit spoiled when it comes to what is considered to be high gasoline prices (and being one I reserve the right to say that), it’s increasingly easy to simply blame the pinch at the pump on the oil companies, and any trick to save money at the pump gets peoples’ attention.  This screed started off as the latter, and in more recent versions has been amended to take a shot at the oil companies.  However, like a lot of crackpot devices that claim to increase fuel economy, this one misses the mark almost entirely.


Spurious gas saving tips
Recently I came across a very useful tip. I was surprised to know it but had a doubt so I talked to one of the pump technicians and he too accepted it as a fact. I think apart from providing space for the gas generated inside the petrol tank this is yet another reason why we shouldn’t fill the tank to the brim. Many of us are not aware that the petrol kiosk pump has a return pipe-line (in Pink). When the petrol tank (in the car) reaches full level, there is a mechanism to trigger off the pump latch and at the same time a return-valve is opened (at the top of the pump station) to allow excess petrol to flow back into the pump. But the return petrol has already pass through the meter, meaning you are donating the petrol back to the Oil Dealer.Also only 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 petrol, when it gets warmer petrol expands, so buying in the afternoon or in the evening….your liter is not exactly a liter. In the petroleum business, the specific gravity and the temperature of the petrol, 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 vapours that are created while you are pumping. All hoses at the pump have a vapour return. If you are pumping on the fast rate, some of the liquid that goes to your tank becomes vapour. Those vapours 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 Petrol tank is HALF FULL. The reason for this is the more Petrol you have in your tank the less air occupying its empty space. petrol evaporates faster than you can imagine. petrol storage tanks have an internal floating roof. This roof serves as zero clearance between the Petrol 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 litre is actually the exact amount.

Another reminder, if there is a petrol truck pumping into the storage tanks when you stop to buy Petrol, DO NOT fill up; most likely the petrol is being stirred up as the Petrol is being delivered, and you might pick up some of the dirt that normally settles on the bottom.


Detailed Analysis

Before even looking at each claim individually, let’s get one thing out of the way first: not one of the items listed in any way was put in place to screw over the consumer and make oil companies richer.  This seems to be a misconception the author had specifically regarding vapor recovery systems.  Aside from the ecological benefits of such systems, if anyone benefited it would be the local filling station owner.  And considering the rather high cost of installing and maintaining those systems – a recent estimate is that the removal of those systems would SAVE filling stations about $3,000 a year.

This newest version starts off with a claim that a mechanism in the pump returns fuel to the underground tank if you fill your vehicle’s tank too much.  It starts off with what is actually a valid premise (“providing space for the gas generated inside the petrol tank” is sound advice to ensure proper functioning of your vehicles evaporative collection system); beyond that, it is well intentioned but pretty inaccurate.  Referring to the ‘pink hose’ would indicate they are referring to a vapor recovery system, although the same principle can be applied to the simple vacuum system used in nearly all common fuel pumps to flip the filler nozzle off.  Of course vapor recovery systems are not universally used; in the US they would only be found in areas designated by the EPA as ‘nonattainment areas’, or in states that mandate use of such systems.  With both vapor recovery systems and the normal vacuum controlled shut-off, the vacuum is created by the negative pressure created in the underground tank as fuel is pumped out and into your vehicle.  It is not an accessory pump designed to suck fuel back out of your tank – those would only be found at tank farms on tanks holding tens of thousands of gallons.  If you look at the nozzle of the fuel pump, you’ll notice a small hole.  In a pump with a vapor recovery system, you’ll notice a couple of larger holes on either side, or a series of holes all the way around the end of the nozzle.  The vacuum created draws air back through those holes.  An interruption in the airflow, or having to ‘suck’ harder, trips the switch to shut off the pump.  Neither system is designed to draw fluid back through the system.  Introduction of liquid can actually foul the system.  Which is where that first paragraph almost gets it right:  hang up the pump when it clicks itself off.  Topping off the tank is bad for your car and bad for the pump and potentially bad for the environment.  Your vehicle’s evaporative control system is designed to re-burn vapor, not liquid fuel, and you could damage it and worsen your vehicles fuel economy.  The vapor recovery system is designed to pull vapor back into the system, but it can and will simply suck fuel you paid for into the vapor recovery system.  And the auto-shutoff on the pump is designed to suck air.  Introduction of liquid can foul that system and prevent the shutoff from shutting off, resulting in you getting a shoe full of gasoline. 
Two other things to note on that subject:  First, neither the auto-shutoff nor the vapor recovery systems are some sinister attempt by the oil companies to try and sell the same fuel twice.  The former was a safety device designed to prevent overfilling and spilling fuel – a safety and environmental hazard.  The latter was mandated by the EPA (and some states) as a stop-gap measure to limit the pollution caused by evaporation of gasoline at filling stations.  Second, the EPA has already started removing the mandates for vapor recovery systems because they are now an expensive redundancy;  the aforementioned evaporative control systems in automobiles makes vapor recovery at the pump unnecessary.

The science behind the ‘fill up in the morning’ advice might seem sound, but in reality it only really matters if you’re a) getting your fuel from an above ground tank, or b) referring to heating oil delivered by a tanker truck.   In the latter case, temperature compensators are used by a number of fuel oil distributors in the US on their delivery trucks, and the invoice will state that volume delivered has been adjusted to the volume of 60 degree Fahrenheit (in the US the reference temperature for petroleum products is 60 degrees F).  There has been talk in some US states of implementing temperature compensators on retail gasoline pumps, but so far the math has not made it that imperative.  Why?  Because underground tanks are 15 to 20 feet below ground.  While surface temperatures may vary 10 or 20 or even 30 degrees (Fahrenheit), the temperature inside a double-welled, insulated fuel tank 20 feet below ground might not even vary a couple of degrees from the usual 55 degrees F.  The only time it will vary significantly is when fuel is being delivered to the underground tanks by a tanker truck.  On a hot day, the fuel from that truck will be warmer and might take a few hours to cool.  Other tests noted that there was a temperature difference between the first few gallons pumped, rapidly cooling to ‘tank temperature’… because fuel is sitting in the pipes and hoses closer to the ground or in the pump itself between fill-ups.  But that was at a test track – not at a busy station, so probably not an issue.  But – for the sake of argument, let’s say you live in a terrifically hot climate and happened to stop in the afternoon when the fuel was potentially at its warmest.  And let’s compound that by having the 10,000 gallon tanker truck just having finished refilling the station’s tanks.  Now, let’s throw all logic aside and say that instead of 60 degree fuel, you’ve got 85 degree fuel.  How much difference does that make?  Let’s say your vehicle has a 20 gallon tank.  Instead of pumping 20 gallons of 60 degree fuel, you’d only get 19.708 gallons of 85 degree fuel.  In a more realistic scenario, the temperature differences noted in real life experiments only varied by a few degrees F.  But for arguments sake, let’s say the tank temp rose to 70 degrees Fahrenheit on a hot afternoon.  That same 20 gallons is now a mere 19.884 gallons.  At a US $4.00 per gallon, that’s less than 50 cents.  Certainly that’s important if, like the screed notes, you’re in the petroleum business and trading in millions of gallons.  But is it significant enough for you to alter your schedule or routine?

So far as pumping at low speed… gasoline evaporation is a given.  It’s going to happen and it’s going to happen at a fairly predictable rate.  The question is this:  is the amount you’re losing to evaporation (regardless of whether the area you are in mandates vapor recovery systems – again, this has nothing to do with making oil companies richer) by agitating the fuel as you pump it greater than the amount you would lose to evaporation by taking 2 or 3 times longer to pump your fuel?  Common sense, folks.

Half full or half empty?  I do tell my daughters to not let the fuel gauge drop below ¼ tank… but that’s more wishful thinking that I won’t go out in the morning and find my vehicle with the fuel gauge sitting on E.  We can always hope.  Other than that, the assumption here is that the more vapor in your tank (the less fuel, the more room for vapor) means that the more vapor is potentially lost when you open your gas cap.  Which is entirely contrary to another school of thought; never having MORE than a half tank because the reduced weight will improve fuel mileage.  Not surprisingly, both are fundamentally wrong.  Remember that evaporative collection system in your car?  Pretend it’s not there.  Without it, at worst you might lose 1 (one) gallon PER YEAR to evaporation.  (Formulas for evaporation can be found here… it’s for storage tanks, so grab a calculator).  With that system, vapor loss is negligible.  The half-tank folks are just asking for trouble and chasing rabbits.  With our aforementioned 20 gallon tank, the weight we’d be saving never getting above ½ tank would be a shade over 83 pounds.  I could just leave my Basset hound at home and achieve the same result.  And before anyone jumps on the math there – yes, I realize I calculated the weight of about 13 gallons, and I know that’s more than half of a 20-gallon tank.  Because when your gauge reads ½ tank, you’ve probably actually only got about 1/3 in the tank.  Fuel gauges are non-linear, and that’s just how they work.

So far as filling your tank when a truck is filling the underground tanks… between the filters in place in the underground tanks and the fuel filters in your vehicle, so long as the tanks are properly maintained this is irrelevant. Instead of forwarding spurious and inaccurate information such as this, you and your friends would be better served by sharing links to pages that offer proven methods of improving fuel economy such as and

Importance Notice

After considerable thought and with an ache in my heart, I have decided that the time has come to close down the Hoax-Slayer website.

These days, the site does not generate enough revenue to cover expenses, and I do not have the financial resources to sustain it going forward.

Moreover, I now work long hours in a full-time and physically taxing job, so maintaining and managing the website and publishing new material has become difficult for me.

And finally, after 18 years of writing about scams and hoaxes, I feel that it is time for me to take my fingers off the keyboard and focus on other projects and pastimes.

When I first started Hoax-Slayer, I never dreamed that I would still be working on the project all these years later or that it would become such an important part of my life. It's been a fantastic and engaging experience and one that I will always treasure.

I hope that my work over the years has helped to make the Internet a little safer and thwarted the activities of at least a few scammers and malicious pranksters.

A Big Thank You

I would also like to thank all of those wonderful people who have supported the project by sharing information from the site, contributing examples of scams and hoaxes, offering suggestions, donating funds, or helping behind the scenes.

I would especially like to thank David White for his tireless contribution to the Hoax-Slayer Facebook Page over many years. David's support has been invaluable, and I can not thank him enough.

Closing Date

Hoax-Slayer will still be around for a few weeks while I wind things down. The site will go offline on May 31, 2021. While I will not be publishing any new posts, you can still access existing material on the site until the date of closure.

Thank you, one and all!

Brett Christensen,