TDI 170 PD MPG - DIS / MPG accuracy? (pessimistic)
Had a 170PD for a few months now and was kind of shocked at the mpg of it, especially urban. Very steady motorway driving (with traffic flow but no more than 70) would return high 40s, maybe 50 dead at a push). Coming from a TDI 140 is was a bit of shock where that would return (according to the DIS) amazing figures even for urban/mixed driving. The 170 shows mid 20s if you do a short urban trip vs over around 40 in the 140 (all DIS figures).
However [in the 170] I put in £25 (20litres) when the tank range said 5miles and it did 220miles which at a rough calc is actually about 50.5mpg, yet the computer said around 46mpg average. This got me thinking if the DIS isn't accurate (pessimistic) so waited until I was doing a longer journey and calculate it more accurate by filling the tank and refilling afterwards.
So I've just brimmed the car today, reset the trip (the one in the speedo dial), and also Computer 1 then drove to central Birmingham and back from Manchester which included some urban driving onto and after the motorway either end. Where possible I set the cruise at 70, there was an accident southbound which slowed progress, and then an accident northbound too...which meant I was in crawling traffic a few times and then used an alternate route back home (A34 which is a-road with a bit stop start).
Getting back I went straight back to the petrol station (188 miles), brimmed it again and it used 15litres exactly; that's 57mpg(!). The DIS showed 49.5mpg average. The fuel level dropped to between full and 3/4 (so used 1/8th according to the gauge).
I'm wondering if the 170 DIS for some reason is just pesimistic, and maybe the 140 DIS is a bit optimistic?? Either way I'm pleased with the results.
It may be worth mentioned the car has the DPF delete BUT the DIS figures were the same before for mpg same kind of driving.