General temporary high comsumption

[Simonosteopath]

Hi,
I have a 3 yr old Fiat 500 Multijet diesel and very pleased in general I am! The economy is great as I regularly achieve indicated average journey consumption figure of 62 to 66mpg.
However, I've noticed if the display is on constant mpg reading, occasionally it will fall to a reading of about 35 to 42 mpg for about 5 minutes, and then return to its typically high figures. It does this 2 or three times per tank-full. Is this anything to do with a particulate filter? Is it normal? No other lights illuminate when this happens.
Thanks for anyone's input!

 

[Robnw67]

Would this just be the usual variation in fuel usage that depends on the load on the engine? When I borrowed the twin air and took my 3 pie eating chums out, I had the instantaneous mpg down to 11mpg going up steep hills and 99mpg down the other side. As long as the average is what you expect, it doesn't sound like anything major.

 

[rkt2003]

Hi,
I have a 3 yr old Fiat 500 Multi jet diesel and very pleased in general I am! The economy is great as I regularly achieve indicated average journey consumption figure of 62 to mpg.
However, I've noticed if the display is on constant mpg reading, occasionally it will fall to a reading of about 35 to 42 mpg for about 5 minutes, and then return to its typically high figures. It does this 2 or three times per tank-full. Is this anything to do with a particulate filter? Is it normal? No other lights illuminate when this happens.
Thanks for anyone's input!

Yes this would pretty much be normal my mjet 500 also did this without lights on the display as it regenerates the dpf cycle.

 

[SteveTDCi]

Yes this would pretty much be normal my mjet 500 also did this without lights on the display as it regenerates the dpf cycle.

I'd have gone for that theory too, the DPF re-gen basically involves piling lots of fuel through the system to burn off and wash away the soot. On the Focus it will only go into re-gen mode if there is more than 1/2 tank of fuel.

 

[Simonosteopath]

Thanks rkt2003.
That's put my mind at rest and completely fits the symptoms and expectation! I found a brief explanation in a handbook too.
Simonosteopath