© Depositphotos.com/ Paul Fleet
By David M. White
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.
Last updated: July 15, 2013
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