पेट्रोल दोपहर को १०% कम मिलता है , रात या सुबह ही ख़रीदे
There is a common understanding that filling fuel at night or during the early hours of the morning is more beneficial as petrol is much cooler at these times meaning less of it will evaporate when re-fueling your vehicle. It’s also common knowledge that when petrol is at a low temperature, it contracts thus occupying less space. At a higher temperature it expands and occupies more space.
A certain volume of fuel, once combusted gives off a certain amount of energy. When that same volume of fuel faces a lower temperature it contracts and occupies less space and in turn less volume. However, it still retains the same chemical composition to give off the same amount of energy before it’s change in volume. What this means is that when pumping at night or early morning, your actually getting more energy in the same amount of fuel as you would if you had done the same during the afternoon.
The logic of this theory is undeniable, however there is a significant amount of evidence to support the contrary. You see at a petrol station, fuel is stored in a non-metallic reservoir or a tank at about 4.6 to 6 metres below the surface. At such a depth and taking into account the non-metallic nature of the storage tank, it would take many hours before the heat produced from the sun during the day to penetrate and heat up the petrol. This is not to say that it can’t happen. It might happen however the differences in fuel quantity and composition is almost negligible.
In the tank, fuel is kept at a relatively stable 12.6 degrees Celsius and petrol has the ability to stabilise its temperature fairly quickly. So it is possible for you to gain or loose a little fuel depending on the time of fill up, but the amount is negligible as at the most you may get 1 per cent more on a good day. If you take into account the time and distance that you need to travel to get to a petrol station at the required time from your location, the advantage is negated. It’s also said that a petrol pump measures fuel based on volume and petrol companies to have a plan to counter such an issue as change in volume. So based on this theory, during lower temperatures though you get more energy in the same amount of fuel, the pump is able to counter the advantage by adjusting the volume accordingly.
So while we cannot rule out the possibility of slight expansion or contraction, the effects are infinitesimal and are not worth the wait. So if you need to fill up before your journey back home this Raya, our advice to you is fill up as and when the need arises. On a long journey, petrol stations are few and far between, it would be unwise to try and manage till the evening or early morning before your next fill up.