What causes MPG to decline over time?

imightbewrong

Yes the problem typically happens if the auto box decides it needs to drop down a gear to maintain speed on the incline.

Trollslayer

Not quite answering your question but I found out by accident that BP regular diesel gives my Peugeot about ten percent better mileage and better acceleration compared with supermarket diesel.
I think it is to do with additives and from what I found out Shell seems to be the same.

gizlaroc

Did you check your thermostats are working correctly?

If they are not, your car will not regen fully and you will be burning loads of fuel while it constantly tries.


I would consider this as well...

Archoil AR6200 Combustion Catalysts / Burn Rate Modifier & Lubricant

Be careful with redex etc. as you need a low ash modern version like above with a DPF.

I will take a photo of my EGR after 90k miles using that stuff, it looks like new.
It has had an electrical failure however. Haha


This explains how well it works, start at 2m44secs...

imightbewrong

Update - after a bunch more engine fault lights we bit the bullet and got the DPF replaced.  Touchwood since then we haven't had any engine faults (we can now accelerate up hills and overtake again) and based on the first few tanks we have gone back from 300 miles to 5-600 miles full to empty.

Hopefully this is it solved and we get a good few more years out of it.

Trollslayer

How many miles had the DPF done?

imightbewrong

85K (i.e. all of them)

Probably c. 65K-70K at the point where symptoms started to appear

Trollslayer

That reminds me, I need to give the car a good run.
My trip to and from work is only 6.5 miles so that isn't enough to get things warmed up, weather like this isn't good for much else.

outoftheknow

Aussies not so keen on manufacturers demanding owners keep the DPF clean. There is a class action starting here over DPFs and the fact they clog etc. doesn’t seem to worry the lawyers that the manuals go on about longer runs to regenerate etc. the argument here is they aren’t fit for purpose. They should filter diesel particulates for the life of the car without the user worrying about short journeys.

Could be interesting over here

mikeysthoughts

Air filters require cleaning and eventually replacement, why would DPFs be different?

imightbewrong

AIr filters are consumable parts - and cost a few quid.  DPFs are not 'designed' to be replaced - they are supposed to self-clean and do as long as you do the right ratio of 'long trips'.  If you don't, then you have to pay £000s * the price of an air filter to do a major engineering job.