Good Motoring
Keep the tank topped up
H. Kishie Singh 

While driving to Delhi on N.H. 1, when you come down over the Ambala flyover, the Indian Oil depot is on the left. The huge reservoirs can be seen from the flyover and in case you missed them, you will surely see oil tankers, a hundred or more, waiting to fill up. They are there in the evening; they fill up at night, when it is cool, and by early morning, they are gone.

Why do they refuel in the cool of the night? Because cool petrol is dense; when the temperature rises, petrol expands. So a litre is not really a litre. In the petroleum business, the specific gravity and temperature of the fuel, be it petrol, diesel, LPG or ethanol, play an important role. A one-degree rise in temperature makes a big difference. It is for this reason that you are advised to refuel either in the morning or evening when the temperatures are cool. During summers when day temperatures can be close to 40 degree C, a fair amount will be lost to evaporation, in addition to the fact that expansion will have shrunk the litre. Money lost.

Chandigarh now has self-service petrol stations. This is where you can save fuel and money while refuelling. The lever in the nozzle has three speeds for delivering the fuel — fast, medium and slow. Select the slow mode, thereby minimising the vapour that is created while pumping. Most attendants select fast. They want to refuel your car as fast as possible because others are waiting. All nozzles have a return hose to trap the vapour.

If you pump at a fast rate, some of the fuel, especially petrol, that goes into your tank becomes vapour. Those vapours are then sucked into the underground tank. So you are getting a "smaller" litre and less for your money. The petrol station benefits from this; hence the attendants pump at a high speed.

There is a strange syndrome of refuelling in our country. People usually buy 10 or 15 litres at a time. It is a waste of time and money. Your fuel bill at the end of the month will be the same.

It is recommended that you keep your tank full at all times. Refuel when the tank is half full. The reason is simple. In a half-full tank, as opposed to an almost empty tank, there is less air occupying the empty space. The more the air, the greater the evaporation. Informatively, the underground tanks have an internal floating roof, or they are supposed to have this false roof. This false roof serves as zero clearance between the atmosphere and the petrol; so it minimises evaporation. Petroleum companies safeguard themselves against evaporation loss. You can do the same; keep the tank topped up.

Another recommendation. Many times you go to refuel, and there is a tanker discharging fuel into the underground tanks. Do not refuel! With thousands of litres gushing into the reservoirs, the petrol in the underground tanks is being stirred up. All the grit at the bottom of the tank is floating around and the fuel you take on could have some grit in it.

This is another very good reason to refuel in the morning. The tanker delivered fuel during the day, and if you refuel in the morning, the grit has had 8-10 hours to allow the grit to settle down. You will get cleaner fuel and a full litre for your money.

There is also an auto-cut facility on the hoses. There is a sensor in the nozzle, which senses that the tank is full and stops delivery automatically. Reason: it leaves a little space for the fuel to expand. Attendants will then pump in a few extra points to round off the figure of the payment. No good. It is a common sight to see the drivers of sarkari Ambassadors rocking the car till the petrol is full to the brim. A very foolish move. He would then drive the sahib to work and the car would be parked for hours in possibly 40 degree C heat. The petrol will expand and spill out. A waste of petrol plus a potential fire hazard that could blow everyone sky high, and all for, maybe, an additional quarter litre of petrol!

Happy motoring.