Filling your petrol tank past “first click”

With petrol prices hovering around all-time highs in 2018, much advice on how to save petrol has been dispensed by one driver to another.

One of the long-standing pieces of advice is “do not fill your tank past first click”.

First click, also called auto stop, is when the petrol pump detects that your car’s petrol tank has reached its intended capacity and stops feeding it petrol.

You may see car owners telling petrol attendants to carry on filling up their vehicles while rocking them slightly in an attempt get more fuel into the tank.

But is this a good idea, and should you even fill your tank to first click in the first place?

To find out, MyBroadband spoke to several industry experts on what you should do when putting petrol in your car.

Get out of the car

The AA told MyBroadband that there are many simple steps motorists should follow when putting petrol in their car.

Step one is to get out of the car and ensure the petrol attendant is putting on the correct fuel, and the correct amount.

This requires users to know the difference between 93 and 95 grades of petrol, and diesel – if their vehicles takes diesel.

Motorists must also have their tyre pressures checked when filling up, and regularly check their oil levels.

The AA added that once you have fueled your car, make sure you park it under cover when at work or at home.

Leaving a car in the South African sun for long periods of time can result in damage to the body paint and the plastic used on the dashboard and other areas.

“First click”

On the matter of filling your petrol tank to the brim, MyBroadband spoke to a car mechanic and garage owner about common misconceptions.

A warning often put forward is that filling your tank past first click will see the “extra” fuel evaporate more easily.

He stated that this is not the case, however, and any evaporation would be minimal.

Another warning put forward is that filling up your tank as much as possible adds more weight to the car – meaning it is less fuel efficient.

The extra weight by adding a couple of litres past “first click” will also be too small to make a significant difference, he said.

At the opposite end of the scale, there are also warnings about driving on a nearly-empty tank.

This includes sediment at the bottom of your tank being picked up as you use the last litres of fuel, and that an empty tank results in the remaining fuel evaporating more easily.

The mechanic dismissed these, too.

Modern cars have filters in place which stop sediment going into your engine with the fuel, while he did not foresee increased evaporation due to an empty tank.

Driving on a half-tank

Another fuel tip put forward is that motorists should drive with under half a tank of fuel, as the weight saving of having less petrol in the tank means the vehicle is more fuel efficient.

A study by Ricardo Inc, cited by The Conversation in 2015, found that fuel economy changes between 1%-2% for 43.5 kg of weight added inside the car.

The report used the 2% difference, and a car with a 60-litre fuel tank and an economy of 8l/100km for its calculations.

It found that petrol weighs 720 grams/l, and the weight of a full tank of fuel is therefore 43.2kg.

This means a full tank will see the fuel economy change to 8.16l/100km – a small difference.

It must also be noted that as soon as your start driving, you will burn more fuel – making your car lighter and more efficient as your trip progresses.

The time it takes to fill up your car on a more regular basis with small amounts of fuel must also be taken into account, along with the danger of running out of fuel before reaching a petrol station.

Now read: South African economy emerges from recession

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Filling your petrol tank past “first click”