Dan:
Your 50mpg might be one of a few things – the weather has warmed up a bit and everyone is seeing better mpg as a result. For the last week or so, when the temps have gotten up to 9 or 10C, I have seen my car get 5% higher mpg than when the day has started at 1 or 2C.
Your commute plays a big factor – the shorter the average journey, the lower your mpg is likely to be. Around 0-2C, my car is taking about 4 miles for the water temp to get to 90C, and about 8 miles for the oil temp to get to 90C. Doing less than 8 miles a day, your car won’t be fully warm by the time you reach your destination, the car is running much less efficient when cold and soot generation is higher, which will fill your DPF and force regens. I have a 12 mile commute, and I have noticed a huge improvement in mpg and regen frequency when I up my miles a bit. If you do 15+ miles for most of your journeys then you should be seeing 50mpg indicated, even in the winter, and most of your regenning will be getting done passively.
Your first regen will stink, it’ll smell like your car is on fire! Most people get their very first one at about 200-250 miles, and then it seems to be anywhere between 200 and 500 miles thereafter, depending on how short your journeys are (and therefore how quickly you’ll fill your DPF) – your car will idle at 1000rpm and not the usual 800. There are other things that will prevent stop-start working, related to battery load. If you’re at a standstill and you’re using your heater or aircon more than a smidge (or heated sets etc) whilst the dipped beam is on, you will usually find your stop-start not kicking in unless the battery is at a very high state of charge (90%).