Examining the true fuel cost of coasting along

Maurice Wadley read through the colourful Department for Transport leaflet that came with the reminder to renew his road fund licence for his car.

It is titled Be a smarter driver and save money. There is obvious stuff such as walking, cycling or public transport (the latter is actually less economical for a car-load).

There is also advice about driving more economically – something many of us overlook if a company is picking up the fuel bill (and why not get buses to slow down?).

What caught Mr Wadley’s attention was: “Don’t coast downhill or towards traffic lights as this uses more fuel. Stay in gear and ease off the gas (sic) gently to reduce fuel flow to the engine to virtually zero”.

Mr Wadley, from Harrogate, who does 2,000 miles a year in his Fiat Punto, comments: “I have always understood that provided the engine is correctly tuned and the foot is not on the throttle, as in coasting, then the engine would be using the least amount of fuel.”

I asked David Ingram, a senior technical manager with Audi. In short, the DfT leaflet is correct.

He says: “If the engine is idling (as in coasting) it is using a small amount of fuel. On the overrun (as promoted by the DfT) the fuel is cut off completely”. The S-Tronic automatic version of Audi’s Q3 has a coasting mode which saves fuel when cruising but allows instant throttle response when needed.