Quick question - does mpg go down if dpf is regenerating ? Normal run to care home on motorway and mpg gets up to about 44mpg mid journey, but only about 30mpg on way back mid journey on same route

Yes, while the DPF is being regenerated, the injectors fire an additional amount of fuel on the exhaust stroke. This causes the DPF to increase in temperature to burn off the soot.
This extra amount of fuel on the exhaust stroke does reduce the MPG while the regen cycle is being carried out.

However other factors are often involved too, like a tail wind in the outward journey, which becomes a head wind on the return journey.

I have this exact phenomenon when I drop No1 daughter to uni in Cardiff. Outward I'll normally have a tail wind, so see 40 ish MPG, however on the return journey a few hours later I'll see mid 30s MPG dispite having less in the vehicle, but I'll be driving into a headwind, which really hampers the MPG. 2009 Rimini Red SE TD4. Soon to be sold.
Gone. 2006 Tonga Green i6 HSE.
Hyundai Ionic 5 Ultimate on order.

Last edited by Nodge68 on 26th Nov 2022 6:06 pm. Edited 1 time in total

Thanks. I guess that was going on then. I did feel my wheels to see of they were warm from binding brakes but all was ok there. Car only gets mainly 60 mile motorway journeys now once or twice a week - and the occasional short into town trip