You too must have at some time or the other heard your friends, neighbors or elders in the house giving advice that “Petrol should always be filled in the car early in the morning, because at that time there is more oil in the tank.”
Their simple logic behind this is that the weather is cold in the morning and petrol is also cold, due to which you get more fuel for the same money. But does this really have any scientific merit or is it just a hearsay misconception? Let us understand the real science behind this 'cold petrol' in simple language…
What is the science of 'cold petrol'?
There is a very basic and simple rule of science that any liquid expands when heated and contracts when cooled. Same thing happens with petrol also. During the day when there is strong sunlight and heat, petrol expands i.e. its density reduces.
What this simply means is that 1 liter of petrol purchased in the scorching heat of the afternoon will weigh slightly less than 1 liter of petrol purchased in the cool of the morning. Based on this logic, people believe that the petrol pump machine gives you more oil in the morning.
Does this actually happen?
After listening to this rule of science, at first glance it seems that reaching the petrol pump early in the morning is a very wise decision. But here people miss a very big practical aspect—and that is the underground storage tank of the petrol pump.
Petrol pump owners do not store their fuel outside in any plastic or iron open tank. The huge tanks that store petrol are buried deep beneath the ground. The temperature under the ground, whether it is 7 in the morning or 2 in the afternoon, remains almost the same and constant. The harsh sunlight or severe cold outside has little to no effect on the petrol present beneath the ground. A test by 'Consumer Reports' also found very negligible (very slight) variation in the temperature of fuel stored in underground tanks between different times of the day. That is, the idea that there is no major financial benefit just by filling petrol in the morning is not completely correct.
So is filling petrol in the morning completely useless?
No, it is not like that at all. If you are leaving with your car in the morning and you need fuel at that time, then you can fill petrol without any hesitation. There is no harm to you in this.
But there is no need to spoil your sleep and go to the petrol pump early in the morning just with the thought that 'petrol will be cooler in the morning and will be available in more quantity'. If your car already has enough fuel in the tank and you are commuting in the morning just to save money, then the savings will be so minor that it will not have any impact on your daily life or pocket.
Disclaimer: This article has been written on the basis of general information and basic rules of science. For better mileage and performance of your vehicle, always follow the service guidelines given by the vehicle manufacturer.