Re: 6k on a grey box. What would you buy?
DPF go back to the early 2000's in some vehicles (and many decades in other types). They should last the life of the car but short journeys kill them and quite often the car along with it due to costs.
The PSA sourced engines use a cartridge of pig wee to clean them, others use extra fuel to burn through (sometimes causing excess fuel in the engine oil which buggers the engine!).
So many different methods. The internet says:
https://en.wikipedia.org/wiki/Diesel_particulate_filter (a bit US biased but gives a rough idea)
Short journeys kill the diesel. Low mileage cars should be checked very carefully. Many bits of freely available software and an 'On Board Diagnostics' OBD plug connected to a laptop will give you a DPF 'life' reading.
After the AA declared ours full and defunct, it actually measured only 17% full - I no longer trust anybody unless I'm looking at an actual live reading on a screen.
The MOT features a visual check so those who remove it and delete it from the cars ECU may come a cropper too.
*As an aside, ours currently has a split in the flexi pipe on the exhaust and is currently much more economical and faster as its not trying to push the exhaust gas through a breeze block... But it sounds like the little engine that could.
We had two Doblos. One was the older non DPF which would get anything up to 65mpg on its display. The later DPF engine barely gets into the 40's with 51 at best despite being the same weight within a few kgs and having the supposedly better engine. The gearing was changed to force the engine revs higher at relatively low speeds in order to keep the DPF clear. But to do that it has to burn more fuel, creating more soot! Aggggghhhhh!!!!!
Wish I'd never bought the damn thing!