Rajan Wilcox
Filling up your gas tank at night or in the early morning is believed by some to be more cost-effective. This is because fuel is denser when it is cooler, and therefore, in theory, you would get more fuel for your money when filling up at these times. However, this theory has been disputed, with sources arguing that the temperature variation between day and night at a gas station is negligible and that the underground tanks keep the fuel at a constant temperature. So, is it worth planning your fuel stops around this theory?
| Characteristics | Values |
|---|---|
| Is it good to fill fuel tanks at night? | Filling fuel tanks at night or early morning may provide more fuel for the same price as fuel contracts in cold temperatures and becomes denser. However, fuel is typically stored in underground tanks that maintain a constant temperature, minimizing daily temperature fluctuations and rendering the time of day insignificant. |
| Fuel characteristics | Fuel expands when heated, making the liquid less dense. |
| Temperature impact on fuel density | The change in fuel density due to temperature variations between day and night is marginal and may not lead to significant cost savings. |
| Fuel storage | Fuel is often stored in underground tanks, which act as insulators, keeping the fuel temperature constant. |
| Industry expert opinion | Rob Underwood, president of Energy Marketers of America, confirms that gasoline dispensers provide a full gallon, irrespective of temperature. |
| Recommendations | It is recommended to refill when your fuel tank is less than a quarter full to avoid fuel pump issues caused by dirt and debris. |
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What You'll Learn
- Fuel is denser when it's cooler, meaning you get more for your money
- Fuel tanks are stored underground, so temperature changes don't affect them
- Fuel in pumps can be warmed by the sun, but this only impacts the first few gallons
- Fuel tanks keep fuel at a constant temperature, so there's no difference day or night
- Filling up when your tank is empty can cause damage to the fuel pump assembly
Fuel is denser when it's cooler, meaning you get more for your money
Filling up your fuel tank at night or in the early morning has long been considered a way to get more fuel for your money. This belief is based on the principle that fuel expands when heated, so filling up when it's cooler means you're getting denser fuel. While this theory makes sense, there are a few factors that suggest the potential savings are marginal at best.
Firstly, most fuel stations store petrol or diesel underground in large tanks beneath a thick layer of concrete, which acts as an insulator and keeps the fuel at a constant temperature. This means that the fuel you pump into your car is likely to be the same temperature, and therefore the same density, whether you fill up during the day or at night.
Secondly, while the air temperature can vary significantly between day and night, the fuel in underground tanks remains at a steady temperature. In one test, the air temperature varied by up to 12° F, but the fuel temperature only dropped by a few degrees over the course of several gallons. This suggests that any difference in fuel density due to temperature would be minimal.
Additionally, today's double-walled tanks are designed to keep fuel at a consistent temperature, so even if the fuel is warm when it's delivered to a station, it will still be warm a few hours later, regardless of the time of day. On busy days, when fuel is being pumped regularly, the fuel in the pipes will also remain at a constant temperature.
While it's true that cooler fuel is denser and you may get marginally more fuel for your money when filling up at night, the actual savings are likely to be negligible. Other factors, such as the extra fuel used to drive to the station at an unusual time, may outweigh any potential savings.
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Fuel tanks are stored underground, so temperature changes don't affect them
The idea that filling up your fuel tank at night or in the early morning is more cost-effective is based on the principle that fuel expands when heated. Therefore, when the temperature is cooler, you get more fuel for the same amount of money. While this theory does hold some truth, the marginal difference is likely not worth going out of your way to fill up your tank at odd times of the day.
While the fuel in the pump dispenser may be warmed by the sun, affecting the temperature of the first few gallons pumped, the temperature of the fuel coming out of the nozzle varies very little, if at all, during any 24-hour period. This is because it doesn't take long for the cooler fuel from the underground tank to be pumped through, replacing the warmer fuel in the lines. On busy days, when fuel is being pumped regularly, the temperature of the fuel in the lines remains constant.
Additionally, today's double-walled tanks are designed to maintain a consistent fuel temperature, keeping fuel warm as well as cool. Therefore, if the fuel is warm when it arrives at the station, it will remain warm when it is dispensed, regardless of the time of day. Furthermore, gasoline pumps are designed to dispense a full gallon, irrespective of temperature.
In conclusion, while it is true that fuel expands when heated, the underground storage of fuel tanks means that temperature changes have a negligible effect on the fuel's density. Therefore, filling up your fuel tank at night or in the early morning will not significantly impact the amount of fuel you receive.
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Fuel in pumps can be warmed by the sun, but this only impacts the first few gallons
Fuel expands when heated, so the theory goes that filling up your car at night or in the early morning when the temperature is cooler will get you more fuel for the same amount of money. However, this theory has some flaws. Most fuel stations store petrol or diesel underground in large tanks beneath a thick layer of concrete, which acts as an insulator and keeps the fuel at a constant temperature.
While it is true that fuel expands when heated, making the liquid less dense, the change in cost savings is marginal. Fuel in pumps can be warmed by the sun, but this only impacts the first few gallons. Over a few summer days, the temperature of the fuel in an underground tank remained steady at 62° F. After the first few gallons were pumped, the fuel temperature varied very little between morning and afternoon fill-ups.
For example, the temperature between the first and tenth gallons dropped by 8° F to 17° F. This is because the fuel in the pipes would also be less dense, but similar to a garden hose, the first few litres of fuel might be warmer than the fuel coming from deep within the tanks. On a busy day, when the station is regularly pumping fuel, the fuel coming through the pipes will not be affected by the heat at all.
Additionally, if you go out of your way to refuel at odd times of the day, you may end up spending more money on fuel than you would save. While you may get slightly more fuel by filling up at night or in the early morning, the temperature variation between day and night at an individual gas station is likely to be negligible.
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Fuel tanks keep fuel at a constant temperature, so there's no difference day or night
Filling up your gas tank at night or in the early morning has long been considered a way to get more fuel for your money. This belief is based on the principle that fuel expands when heated, so filling up when it's cooler means you're getting denser fuel. While this theory makes sense, there are a few flaws.
Firstly, most fuel stations store their petrol or diesel underground in large tanks beneath a thick layer of concrete. This concrete acts as an insulator, keeping the fuel at a constant temperature regardless of the time of day. Tests have shown that even when the air temperature varies by up to 12° F between morning and afternoon, the fuel in underground tanks remains at a steady temperature. As a result, the temperature of the fuel being dispensed varies very little throughout the day.
Additionally, today's double-walled tanks are designed to keep fuel at a consistent temperature, whether that's warm or cold. So even if the fuel is warm when it's delivered to a station, it will still be warm a few hours later, regardless of whether it's dispensed at 5 am or 2 pm.
While it's true that fuel expands when heated, the potential cost savings from filling up at night or early morning are marginal. In fact, if you have to go out of your way to find a fuel station at these times, you may end up spending more on fuel than you save.
Therefore, while the theory behind filling up at night or early morning is sound, the reality is that fuel tanks keep fuel at a constant temperature, so there's no significant difference in the density of the fuel you're getting, regardless of the time of day.
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Filling up when your tank is empty can cause damage to the fuel pump assembly
There are several opinions on whether filling fuel tanks at night is a good idea. One popular belief is that since fuel expands when heated, filling up during the early morning hours or late at night when the weather is cooler can get you more fuel for the same price. However, this theory has a flaw. Most fuel stations store petrol or diesel underground in large tanks beneath a thick layer of concrete, which acts as an insulator, keeping the fuel at a constant temperature.
Now, while filling up a fuel tank at night may or may not get you more fuel, doing so when your tank is empty can indeed cause damage to the fuel pump assembly. Here's how:
When your vehicle's fuel tank is empty, or close to empty, the fuel pump will try to suck up the remaining fuel along with dirt, debris, and particles from the bottom of the tank. This can clog up the fuel filter, leading to fuel pump assembly failure. Therefore, it is recommended to refill your tank when you have a little under a quarter of a tank left.
This issue is common in Toyota FJ Cruiser vehicles, where the fuel pump replacement can sometimes lead to inaccurate fuel gauge calibration. The fuel gauge sending unit is attached to the fuel pump assembly and is actuated by a float on a stiff wire 'arm'. If this wire arm is bent during the replacement process, it can result in a faulty fuel gauge.
To avoid this issue, it is important to ensure that the wire arm is not damaged during the removal and reinstallation of the fuel pump assembly. It is also recommended to have the work done by someone familiar with the vehicle's fuel pump and fuel gauge sender setup, who can competently remove and replace the assembly without causing any damage.
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Frequently asked questions
Yes, it is true that fuel expands when heated, so filling up your tank when it's cooler out will mean you're getting denser fuel. However, the change in cost savings is marginal, and fuel tanks are often kept underground, where the temperature stays constant.
It's best to fill up your gas tank early in the morning or late at night when the weather is cooler. Fuel contracts in colder temperatures, so you'll get more for your money.
While fuel is denser in the morning, the temperature difference between day and night at a gas station is negligible. The temperature of the fuel in the underground tanks remains steady, so you're not getting more fuel for your money.
No, waiting until your tank is empty can cause serious damage. If your gas tank is empty, your vehicle's fuel pump will try to suck up dirt and debris along with the last bit of fuel, which can clog the fuel filter and lead to fuel pump assembly failure. It's better to refill when you have a quarter of a tank left.
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