Filling petrol in the day or night

  • Thread starter jablonsky27
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In summary, filling your car with petrol at night may seem like a good idea because the cooler temperatures could potentially result in a slightly larger volume of fuel. However, in reality, the temperature of the fuel at the point of metering does not change significantly, so there is no noticeable difference in the amount of fuel you receive. While there may be some countries where buying fuel at a lower temperature could result in a denser fuel and potentially save money, this is not the case in most countries where fuel is sold by volume rather than mass. Additionally, the way fuel pumps measure flow does not rely on fluid speed, making the argument of a larger cross-section of the tube in warmer temperatures invalid. Ultimately, it does not make a significant difference
  • #1
jablonsky27
74
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hi,
my friend told me the other day that it makes more sense to fill petrol in your car in the night instead of in the day.
he says, that since its generally cooler in the night, the volume of petrol you get is more than what you would get if it were daytime instead, since its warmer. so u get slightly more fuel and a better mileage.

my take is this : whether day or night, the amount of petrol(moles) you fill in your car doesn't change. so it doesn't make any difference.

what makes more sense?
 
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  • #2
In theory, your friend has the right idea, but in practice, it doesn't work that way. Most gas tanks are buried in the ground, and the gasoline is insulated well enough that it won't change temperature noticeably over the course of the day or night. Fill up your car whenever you want - it won't make any difference.
 
  • #3
Winter, at least in the USA. Energy content is a proportional to fuel mass, not fuel volume. US fuel stations charge per unit volume, not per unit mass. Since fuel density decreases as temperature increases, it is better to buy fuel when temperature is lower. YMMV (literally!) in other countries. Some countries mandate a temperature-based adjustment to the measurement of the quantity of delivered fuel.
 
  • #4
I'm not sure how the volume of the fuel is measured. If the device would always measure the correct volume, then it would make more sense to buy dense petrol. But maybe it is not so: maybe the volume flow is calculated from measured value of the speed of the petrol? Then higher temperature would also increase the cross-section of the tube, so you could get more volume for the same price.
 
  • #5
Your friend is right. However, as Turbo has stated, the temperature of the fuel at the point being metered generally doesn't change much, so only a very small difference would be measurable (and probably not noticed).

Lojzek's theory is nice but not correct. Fuel pumps don't calculate flow from fluid speed; they measure the flow directly (volumetrically) using a flow meter.
 

Related to Filling petrol in the day or night

1. What is the best time to fill petrol, day or night?

The best time to fill petrol is during the day when the temperatures are cooler. This is because petrol is denser in cooler temperatures and you will get more fuel for your money. Additionally, petrol stations tend to be less crowded during the day, making it a quicker and more convenient process.

2. Is it safe to fill petrol at night?

Yes, it is safe to fill petrol at night. Petrol stations are well-lit and have security measures in place to ensure the safety of customers. However, it is always recommended to be aware of your surroundings and take precautions, such as locking your car doors and not leaving valuables in plain sight.

3. Why is petrol more expensive at night?

Petrol prices are not necessarily more expensive at night, but they may appear that way due to the increased demand during peak hours. This is because more people are likely to fill petrol after work or during their commute, causing an increase in demand and potentially higher prices. It is always best to compare prices at different petrol stations to find the best deal.

4. Does filling petrol at night affect my car's performance?

No, filling petrol at night does not affect your car's performance. The quality of petrol remains the same regardless of the time of day it is filled. However, if you are filling petrol in extremely cold temperatures, it is recommended to let your car warm up for a few minutes before driving to ensure proper fuel circulation.

5. Can I fill petrol at any time during the day or night?

Most petrol stations are open 24/7, allowing you to fill petrol at any time during the day or night. However, it is always best to check the operating hours of your preferred petrol station to ensure they are open before making a trip. Some petrol stations may have limited hours or be closed for maintenance during certain times.

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