I'm about to start a new job that will mean a weekly round trip of 240 miles in my 2010 SLK v6 auto petrol Merc. It's going to be just once a week and mostly motorway driving. However, having been mostly been doing much shorter trips since owning the car I'm not sure how costly that's going to be in petrol, economy, taking age into consideration etc. Anyone doing , or has done a regular similar commute?