The results of the Swiss Harmony CarTuner test were impressive.

On the first outward journey to Edinburgh we drove 653 km and consumed 34.77 liters of diesel. This corresponds to a fuel consumption of 5.3 l/100 km.

On the way back to London it was 661 km and we filled up with 39.67 liters. This corresponds to exactly 6 l/100 km.

The second trip to Edinburgh with the built-in CarTuner resulted in a fuel consumption of 4.1 l/100 km. This corresponds to a saving of 22%.

On the way back to London with the built-in CarTuner, we consumed 33.66 liters, the equivalent of 5.1 l/100 km. The saving was 15%.

Here you can see the data at a glance:

Without CarTuner With CarTuner Savings in %
From London to Edinburgh (406 miles) 5.3 l/100 km 4.1 l/100 km 22%
From Edinburgh to London (414 miles) 6.0 l/100 km 5.1 l/100 km 15%