During passive regeneration, only a portion of the particulate matter is converted into carbon dioxide. This is because the chemical reaction, which utilises nitrogen dioxide, is slower than the rate of engine production of particulate matter and is effective from 250°C (482°F). Above 580°C the conversion efficiency of the particulates into carbon dioxide rapidly increases. These temperatures are generally only be achieved using the active regeneration process.
This is the reason I said above that it's not just short journeys. The quote is from the downloadable DPF document dated 15 May 2015 - "Exhaust System - INGENIUM I4 2.0L Diesel - Diesel Particulate Filter - System Operation and Component Description". My interpretation of this technical narrative is that even if you were pulling 2500 Kgs of Shire Horse up Mount Snowden, i.e. getting the exhaust really hot, the passive regen would not be sufficient to get rid of all the soot and therefore an active cycle would still occur, at the latest, by 250 miles. And that's when the real dilution occurs. The thing is this. If, like me, you're happy pootling safely along A roads at 50-60 mph, or Motorways at 65-70 mph, then your driving style is going to make the system invoke active cycles on a much more frequent basis and, bingo, there goes your promised 2 year service schedule right there and here comes an oil service every 10-12K miles. What the hell would you have to do with this engine to get, say, 15K miles between services? Has anyone actually gone further than 75% of the promised mileage before needing a service? This would start to look like class action territory were it not for JLRs willingness to change the oil for free for anyone who asks - just like they did a year ago with the Evoque . So everything is ok, then?
No, because there's another great big elephant in the room in the form of all the experts who think that 2% is the maximum safe value for diesel dilution. This view of the world says that, if you run your DS for 12,000 miles and then change the oil because it has (let's be generous) 6% diesel content, you have just treated your engine to 8,000 miles of driving with progressively worsening, sub-standard lubricant. I am so glad I joined this commhnity, saw this threat coming and acted when I did.