Ask Honest John

Honest John Ask Honest John » Should I trust my Mondeo's trip counters or my own calculations when measuring mpg?

Should I trust my Mondeo's trip counters or my own calculations when measuring mpg?

I have owned two cars from new with trip computers, both of which were over-optimistic about fuel consumption. Typically in my 2008 Mondeo diesel I achieve 47mpg by doing brim-to-brim calculations. The trip computer always eventually settles around 52-53mpg when my driving is mixed, including motorways and town driving. People often quote their car's mpg to me based on the trip computer but I am usually sceptical. Are some better than others?

Asked on 16 June 2012 by PJ, Altrincham

Answered by Honest John
Your odometer might not be correct either. My Mazda 5 measured a regular trip I have to make as 294.5 miles. Others have measured it at as much as 312 miles. The average is 300 miles. On cruise control at 50 or at 70 I found myself overtaking other cars. So I conclude that the Mazda is closer to accurate than any other car I have driven, and I can't safely drive at 75-80 on the speedo using the standard margin for error.

Real MPG enables you to register the fuel economy you are actually getting against your make and model of car, its engine and type of transmission.

Every time you enter an average consumption figure against your car, the overall average automatically adjusts to reflect it.

Real MPG
Similar questions
Now that we have better quality sensors and electronics, is it not possible for car manufacturers to fit accurate speedometers? On a section of road works where the speeds are closely monitored, most drivers...
I filled up today and started to calculate my mpg using the trip meter reading, when it occurred to me that it is probably as inaccurate as the speedometer itself (in my case about 7-8per cent optimistic)....
I've just bought a new 61-plate Toyota Prius which has a completely electronic dashboard display. Checking the speedo against a SatNav, it showed that at a constant 70mph indicated (held by cruise control...
Related models
Very good to drive. Refined and comfortable to travel in. Massively roomy cabin and huge boot. Reasonable value. Efficient ECOnetic and EcoBoost models.