Before we start this is not a DPF delete or DPF rules and regs post!

I have a simple question for those of you who do lots of miles in you diesel BMW's.

I have a 330d, I am now regretting buying it as it only does short journeys, we have had it a year now and I scanned it tonight with Torque app, I noticed the coolant temp is around 75'C nearly all the time so the thermostat is knackered, I also found out the car has an error code P14a7 DPF Flow Resistance Too High.

So tonight I have been for a long journey held the auto in 4th and drove at 75mph to try and clear the DPF, after 10 miles the temp never went up, I stopped in a lay by and held the revs at 2000 for 20 minutes, temp hit 93'C and you could see on the app that engine load reduced from 26% to 22% I then drove home and temp stayed up above 88'C.

Two questions, first is why would the temp stay high after it got up there but not before? second How do you know when a BMW is regenerating its DPF? I had an Audi and when it did the DPF regen the engine would idle at 1100 rpm, cooling fans would be on full and the throttle would be very responsive, does the BMW do this?

Thank you for reading and I look forward to your replies.