Hi Monkeyhanger - you have mentioned regen in a couple of your posts. Can you help me and advise what that is please? Sorry only got the car this week and fairly new to the forum. Thanks.
Regeneration of the DPF. There is a multilayered ceramic block (think of it like a honeycomb, but it's structure is more uniform than that) just after the engine manifold, at the start of the exhaust system through which the exhaust gases flow. It collects all the soot generated by the engine and stores it so you don't get that sooty black cloud pouring from your exhaust that can be seen in older diesels.
At intervals the DPF needs to be cleared so the exhaust back pressure doesn't build up.
If you do regular moderately long journeys, the engine generates enough heat for the DPF to heat up and burn off the soot. This is passive regeneration, if you do more than 15 miles per journey then this should suffice to keep the DPF clear, this can't happen until the engine is up to full operating temperature.
Then there is active regeneration. Basically the DPF is loaded with soot to the point where the car tries to force a regen because you persistently haven't met the conditions for a passive regen. It takes steps to force the DPF up to temperature required for regen by introducing fuel into it to burn and generate heat independently of the engine.
During active regen the car is running (in my experience) about 15% thirstier than normal. When the DPF is clean, post regen, the car will be running at its most economical, and it starts to dip towards the point at which regen is required. On my 12 mile commute, I can see 47mpg for the journey when the DPF is clean, dipping down to about 45mpg when a regen is imminent, and 41mpg when undergoing an active regen.
