[AlanHo]

I have just driven down to Bristol on the M42 and M5 motorways and decided to do a careful check of the car’s economy for the trip down. As it happened – sods law kicked in and when we set off this morning the car displayed the message “Auto Save Deactivated” which means the DPF had decided to regenerate from the outset. It last regenerated roughly 265 miles ago – it is difficult to tell when you are cruising on a long run because the only indication is the economy trip suddenly shows a significant increase in fuel consumption. Whereas about town the engine stop/start being deactivated is a good give-away.

Anyway I am at a loose end in the hotel - so it will fill my time by recording what happened today – so here is the result.

Odo 6105   Set economy trip to zero upon leaving home. Display showed “Auto Save Deactivated.

Odo 6109   Joined M42 motorway and gently accelerated to 60 mph. Trip average read 33.2 mpg and instant economy bar graph was varying between 30 to 40 mpg.

Odo 6131  Instant economy graph suddenly went off the scale above 50 mpg. DPF regen must have ended. Average economy trip read 38.1 mpg at this point and was now gently climbing.

Odo 6203   Left the motorway having cruised at 58 to 65 mph without using the cruise control. Average economy trip read 57.5 mpg.

Assuming that the trip recorder is accurate it is now possible to calculate the average economy for the sector on the motorway after the DPF finished regenerating - as follows :-

Total journey distance = 6203 - 6105 =  98 miles
Total fuel used = 98/57.5 = 1.704 galls

Distance travelled with DPF regenerating = 6131 – 6105 = 26 miles
Fuel used = 26/38.1 = 0.682 gallons

Distance on motorway after DPF regen ended = 6203 – 6131 = 72 miles
Fuel used in this sector = 1.704 – 0.682 = 1.022 gallons
Hence economy in this sector was 72/1.022 = 70.45 mpg

This proves that the combination of me driving my car, with two up, at 60 to 65 mph, on a motorway, on a hot sunny day, can achieve excellent economy near to the government official figure.

However – the DPF on my car regenerates on average every 250 to 300 miles. The regeneration lasts for 20 to 25 minutes or approx. 25 miles. Today suggests that economy during the regen period is 38 mpg when it occurs on a motorway.

From previous road tests I have determined that my car averages about 45 mpg (6.27 l/100k) in the city, 60 mpg (4.71 l/100k) on A roads and now it seems 70 mpg (4.04 l/100k) on a motorway easy cruise and 38 mpg (7.43 l/100k) when the DPF is regenerating.  This gives me some basic data to calculate what my overall economy should be for each 250 mile DPF regeneration cycle for my monthly typical use of the car, calculated as follows :-

25% city driving      = 62.5 miles @ 45 mpg = 1.39 galls used
35% on A roads      = 87.5 miles @ 60 mpg = 1.46 galls used
40% on motorways = 100 miles @ 70 mpg  = 1.43 galls used
DPF Regeneration   = 25 miles @ 38 mpg    = 0.66 galls used
Totals : 275 miles using 4.94 gallons = 55.66 mpg (5.08 l/100k)       

This calculated average of 55.66 mpg (5.08 l/100k) is surprisingly close to the average economy of my car to date which is 54.87 mpg (5.15 l/100k) over 6105 miles.

From the above figures you can calculate that if I was in Australia and did not have a DPF the economy would average 59.42 mpg (4.75 l/100k) – 7% more - but not quite enough to get me to emigrate.

[Dazzler]

Thanks very much Alan...  (very interesting)

[Phil №❶]

I often wonder what your other half makes of these "trips" and the hotel calculations, some holiday 

But thanks Alan, I think this is a good figure for the average DPF fitted car to expect as a starting point. Naturally all the other variables come into play, driver, weather, traffic roads etc. 

[Lester]

Crikey AlanHo, you certainly do the maths on your trips, have you worked out how many sips you get to a pint of Stella? Or are you a guzzler?  1 guzzle to the pint.

I was in England in 27 April, to 20 May this year, picked up a new Peugot 207 diesel rental car from Thrifty@Southampton, post cruise from Sydney.  The trip computor showed me averaging 60 mpg, very good.  I did 700 miles in 3 weeks, this time only went as far north as Lincolnshire, but spent most of my time in  Devon,Cornwall and Essex/Norfolk.  Just loved the M25, but had driven on it before, albeit in 2004, traffic is heavier now in UK.

[AlanHo]

I often wonder what your other half makes of these "trips" and the hotel calculations, some holiday 

We have travelled south to visit a couple of National Trust stately homes and gardens in the Bristol area and I left her to organise the hotel. 
So what would you be doing whilst madam is in the hotel spa being smothered with mud then having a pedicure etc. other than sit in the lounge with a nice glass of wine and use your laptop. Life doesn't get better than this.........

[Phil №❶]

I often wonder what your other half makes of these "trips" and the hotel calculations, some holiday 

We have travelled south to visit a couple of National Trust stately homes and gardens in the Bristol area and I left her to organise the hotel. 
So what would you be doing whilst madam is in the hotel spa being smothered with mud then having a pedicure etc. other than sit in the lounge with a nice glass of wine and use your laptop. Life doesn't get better than this.........

I can visualize that. When I visited London a long time ago, my mate and I used to travel here there and everywhere during the day, then return to our hotel, sit in front of a lovely wood fire and drink pommie pints,,,, ah the memories. Wish I was ther with you, but I'm stuck in the HOS at the moment.