MOTORING NEWS - Modern vehicle fuel tank systems make provision for the expansion of fuel and the control of fuel vapour, not only to prevent fuel wastage, but also to restrict potentially harmful fuel vapour loss to the atmosphere.
Petrol tends to expand and increasingly give off fuel vapour with time and vehicle operation as it becomes exposed to higher temperatures within the vehicle compared to the fuel filling station's underground storage tanks.
Vehicle fuel tanks therefore have a larger actual volume than the stated capacity. The percentage 'expansion' volume varies between vehicle types, but is typically in the region of 8% of the stated capacity.
Older vehicles' fuel tanks that have breather systems, which ultimately vent to the atmosphere and do not feature a 'closed loop' fuel vapour recovery system, can be overfilled by persistent 'trickle filling', which takes up the expected fuel tank expansion volume. At many fuel filling stations in South Africa forecourt attendants appear to feel obliged to fill customers' vehicle fuel tanks to the maximum extent possible.
The National Association of Automobile Manufacturers of SA (Naamsa) members advise against the 'trickle filling' of vehicles as it may result in:
- Unnecessary waste of fuel to the atmosphere during the prolonged filling of the vehicle with fuel cap removed
- Possible waste of fuel as a result of subsequent fuel expansion in the tank and vapour emission through the fuel tank breather system
- Unnecessary air pollution
- Risk of vehicle paint damage as a result of the inevitable spillage of fuel down the bodywork of the vehicle during the trickle filling process
- Unnecessary delays to motorists at fuel filling stations, particularly during peak holiday seasons.
It is recommended that fuel filling should be terminated at the first automatic pump 'shut off' with the fuel filler set at lowest fill rate.
