So I seem to receive this email about once a month– probably because of my relatively extensive automotive background– and at this point, my frustration with misinformation concerning this topic has reached a head. I know gas is insanely expensive right now (especially to those of us in California), but this sort of rhetoric can spread like wild fire and begin to lull us away from some of the REAL technologies or tips that actually can have a meaningful impact on fuel savings. Moreover, I’d really like to put this to rest… and I guess have a link to send back to the many ill-informed folks buying into this.  

View the intitial email in its entirety here .

Let me start from the beginning: 

“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.”

 This CAN be relatively true, however, the temperature of your car and its tank is what’s relevant here–NOT THE GROUND. The ambient temperature changes of anything more than 6 feet of earth is relative. Its the same reason you don’t notice much of a difference when you use your facet on a hot summer day (that is once you’ve let it run for a bit), or the same reason that the gas doesn’t freeze in the middle of winter- Ambient ground temperatures at twenty feet below the surface just don’t change that much. You should fill up your car in the morning because the CAR IS COOLER… however, it again is relative, because if you park it out in the sun, more gas will evaporate than what you’d save in the “morning ground temp.” Moreover, you’re pretty much hosed in CA, AZ, & NV, because they use SO much alcohol(10% or more) in their gas which evaporates much quicker than other states “normal” gas. It is also VERY important to note that in many states that see winters or more major seasonal changes, they use “seasonal” gases which have different additives and characteristics that respond to climate differentiations. 

“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. “   

FALSE. A 1 degree temp change is not a big deal. The reality is that there is generally a 1-2% shift in gasoline expansion/contraction for every 15 degrees. This is really only important to RACING and Above ground Storage. However, again, this is really more relative to YOUR cars temps. Just beacuse you get a 1/16 more of a gallon in your tank from filling up in the morning, doesn’t mean it gets to your engine. Especially if you fill up in the morning and go park it in an hot, unshaded parking lot for the day. But then again, if you have a black car vs. a white car, you could see other differentiations. Moreover, most states that are hot or use seasonal gas use additives that REDUCE evaporation so that hot fuel lines don’t cause Vapor Lock- which some of you older folks may remember 15+ years ago. Regardless, we’re talking about very minute changes - generally only really taken into consideration when discussing Race Cars (performance only) or storing HUGE amounts of fuel OUTSIDE.  

“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. In slow mode you should be pumping on low speed, 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 other 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. “    

Only a few states actually use a proper vapor return (California is one of them), but the vapor also escapes through you car’s charcoal canister, which makes the above statement false. And if your car is around 1985 or newer, you do have a fuel vapor and charcoal filter system. If its older, it doesn’t matter, because the fuel system isn’t sealed. And while it may save you a few cents (maybe 3-10 cents across 15 gallons), it has no real bearing on how much gas actually goes into your tank. By the way, the purposes of the “vapor vacum” in the California pumps is for environmental issues…and that “vapor” is recycled back into the system, then condenses back into the tank because of the ~50-60 degree temp, and is then passed on the next person getting gas. Its a VERY negligible amount and what goes around comes around.

 

“One of the most important tips is to fill up when your gas tank is HALF FULL or HALF EMPTY. 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.”

 Not many tanks have a “floating roof”…. Maybe a hand full of cars (can’t remember the last time I saw one), and really only race cars - but the “floating” or “bladder” is for safety, nothing else. And again, his experience has to do with LARGE volumes. However, you should never wait until your car is totally empty- its just bad for the cars fuel system, and has nothing to do with “savings.”

“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. Hope this will help you get the most value for your money.”   

 Although this does have some truth to it, there are multiple filters on the gas stations system AND in your car. It really doesn’t make any difference, because half the additives they put in the gas do a great job of clogging stuff up by themselves - hence the average of 2-3 fuel filters in an average car. The reality is, that while some of the above instances can be measured, even if on a SUPER small scale, your car’s condition and your maintenance diligence have WAY WAY WAY ( I mean EXPONENTIALLY) more of an effect on fuel consumption. If all the people reading these emails are really that concerned about MPG’s, they should spend the time checking their tire pressure at the pumps instead of talking on their cell phones. It has been PROVEN time and time again, beyond ANY reasonable doubt, that properly inflated tires and proper oil changes/ maintenance have a HUGE impact on fuel efficiency. This guy is talking about incredibly small variations… not even changes that would register in most tests.A improperly inflated tire can have a ~1-2 MPG drop, and continued use on an improperly inflated tire can lead to other issues that would in turn cause more losses in fuel efficiency.  

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