How far can you drive on a spare?
The fuel reserve indicator is the indicator most disliked by drivers. This means the need to refuel, which is becoming more and more expensive.
The fuel reserve indicator is the indicator most disliked by drivers. This means the need to refuel, which is becoming more and more expensive.
Passenger cars with spark-ignition engines are designed so that with an average fuel consumption of 8 l/100 km they can travel from 600 to 700 km on one tank. Cars with diesel engines, consuming about 6 liters per 100 km, drive 900-1000 km without refueling in favorable conditions. 
The tanks of passenger cars have a capacity of 40 to 70 liters, with the exception of luxury cars with tanks that can hold up to 90 liters of fuel. If the engine consumes more fuel, the tank must have a larger capacity.
All passenger cars are equipped with fuel gauges located on the dashboard within the direct line of sight of the driver. Indicators usually have a scale consisting of four parts and a separate reserve field marked in red. More expensive designs have a fuel reserve warning light. Illuminates when the fuel in the tank reaches the reserve level set by the vehicle manufacturer. It is very difficult to clearly define what a reserve is. It is estimated that in most cars the volume is equal to 0,1 of the tank volume. Currently, manufacturers rarely indicate the amount of the reserve in their technical documentation. From the average fuel consumption and tank capacity of cars operated on our market, it is 5 - 8 liters. This reserve should provide access to the nearest station 
gasoline, i.e. about 50 km.
Many vehicles still have fuel in the tank when the fuel gauge reads "0". Due to the horizontal position of the tank and the large flat surface of the bottom, the engine cannot always run out of fuel.
To check the relationship between the position of the pointer and the actual amount of fuel in the tank, it is necessary to burn the fuel until the engine stalls. However, such attempts carry certain risks. In cars with spark ignition engines, all impurities at the bottom of the tank will enter the filter, they can effectively clog it, preventing the flow of fuel. In vehicles with diesel engines, in addition to the dangers described above, air locks in the fuel system can occur. Removing air bubbles from a system can be a laborious and time consuming process, often requiring a visit to an authorized service center.
Today, the so-called on-board computer is installed in many types of vehicles. One of its useful features is the calculation of instantaneous and average fuel consumption. Based on the average fuel consumption, the device calculates the distance to be driven with the remaining fuel in the tank. The first acoustic signal, informing the driver about the need to go to the gas station in a Ford Focus, is emitted when about 80 km can be driven, and the next - when only 50 km are left. The needle of the fuel level indicator constantly falls down, and the distance to be overcome is constantly displayed on the computer screen. Thanks to the continuous measurement of the amount of fuel and the correlation with the possible distance, this is the best way to inform the driver about the amount of fuel reserve.
Fuel tank capacity of some cars
| Make and type of car | Fuel tank capacity (l) |
Fiat Seicento | 35 |
Daewoo Matiz | 38 |
Skoda Fabia | 45 |
Volkswagen Golf V | 55 |
Peugeot 307 | 60 |
Ford Mondeo | 60 |
Toyota Avensis | 60 |
Audi A 6 | 70 |
Renault Laguna | 70 |
Volvo C 60 | 70 |
Renault Espace | 80 |
Phaeton | 90 |
