"I always thought the whole point of having a diesel engined car was for better fuel consumption. Most modern petrol engined cars will beat that hands down and petrol is much cheaper than diesel too with none of the smell, noise, vibration or inherent problems either. Time to move it on I would say."

Total nonsense. We run a diesel Kia Ceed SW. In 25,000 miles we have averaged 51mpg. Owners of the same car with the pertol engine average about 35 mpg according to various websites.

By my simple calculations we have saved 224 gallons of fuel. Factoring in the 4 pence per litre difference and using todays cost at the pumps we have saved £1296 in fuel plus about £200 in RFL costs, altogether about £1500. Servicing costs exactly the same.

As for smell, noise and vibration you obviously have not driven a modern diesel.

With regards to problems I think that is the luck of the draw. Not had a problem with either a diesel or a petrol ever.

Remember that the OP is driving a S-Max auto and not a small city car. If you can suggest an auto 7 petrol car of the same dimensions that will do better than 33/34 mpg in the same type of use please tell us.

With regard to the Mondeo comparison we had a TDCi 130, the wifes commute was about 8 miles across town plus it did motorway miles to the outlaws and holiday runs. Over 30,000 miles it averaged 38 mpg therefore 34 mpg out of an auto S-Max looks pretty good to me.

Regarding the OP's original question a bit of maths reveals the simple facts. While he has owned the car he has covered 18,000 at an average of 33.3 mpg according to the fuel confuser. That is 540.5 gallons used. Assuming this recent drop has taken place over the last 1000 miles he did 17,000 miles at an average of 33.4 mpg using 509.0 gallons. Bit more maths means he has used 31.5 gallons over the last 1000 miles, yet more maths shows the average for those 1000 miles was 31.75 mpg.

Hardly significant and almost certainly due to the cold weather and the simple fact you always get less mpg out of winter diesel.

Edited by skidpan on 09/04/2013 at 10:55