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Fuel economy dropped off a cliff. Dpf regen?

Craig · 7 · 3227

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Offline Craig

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My fuel economy seems to have been really bad this week. For the last two years my average has been 41.7 mog.  The average suddenly dropped to the mid-30ss, with point mpg readings about 50% of what I usually get it seems to me.  I've been thinking that this is the mystical DPF regen happening, which I have never really noticed before and it certainly hasn't had this much of an effect on economy before. I drive around an hour each way, half and half slow traffic and 50-70 mph.  If regen only happens above 2k rpm then I figure it's still been going for at least three hours so far.

I think I'll check tyre pressures then go boot the nuts off it for a while, but I'm interested in the thoughts of you guys on it.  Initially I thought it was a stuck calliper as I got a whiff of heat at one point after parking, but there's no grinding, lack of roll, or dip in performance.
  • 2010 i30 1.6 CRDi comfort auto (pre facelift) & 2017 Hyundai Ioniq hybrid


Offline AlanHo

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On my three i30 1.6 CRDI manual cars I usually had a dip in economy of roughly 15% during the cold and windy winter months. this was exacerbated by the fact that we did less long journeys in the winter than summer. My cars all regenerated roughly every 250 miles - it took about 20  miles or 20 minutes each time. During regeneration my cars averaged roughly 30 mpg - even on a motorway at 65 mph.

See this old thread for more details.

:link: DPF Regeneration Intervals

I don't know whether you share your car with anyone - but I am very conscious that with my driving style economy is about 10% higher than when my wife drives under similar conditions. I tend to drive with a light right foot, accelerate gently, use the highest gear the car is comfortable with, and always anticipate road conditions a long way ahead to maximise over-run and minimise braking. My wife tend to have a heavier foot, accelerates harder than me and uses the brakes more. It makes quite a difference.


I have never owned an auto i30 diesel hence cannot relate my figures to yours.  However - I would agree yours look high. Have you ever done any brim to brim accurate calculations to confirm your fears. The trip computer often tells fibs.

Another thought - have you recently put winter tyres on?
  • 2017 KIA Niro 2 1.6 petrol Hybrid


Offline Craig

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No changes in circumstances or driving style, or certainly not enough for this much of a difference.  It has been wet recently, but it's pretty much always wet.

I habitually watch the point MPG meter so know in my head at this point what I should be getting at certain speeds, inclines and throttle positions on my commute, and it's been at about 60-70% of expected values this week.

I do 25 miles each way every week day, which can take an hour so the average speed is low-ish, but I'll be at 60mph usually for at least 20 minutes on both trips.  I always figured that this was enough to avoid the need for a regen as I'd never seen the MPG plummet, but maybe it finally built up enough that it triggered one?
  • 2010 i30 1.6 CRDi comfort auto (pre facelift) & 2017 Hyundai Ioniq hybrid


Offline AlanHo

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It is a common misconception that running at 60 mph puts off the need for a regen.

It is just not true.

The faster you go - the more fuel you use and the more soot you create  - thus the faster the DPF gets loaded.

This misconception arises because the manual tells you that if the warning light comes on to tell you the DPF is loaded - go for a fast long drive to correct it. All this does is give the DPF the opportunity to regenerate that your previous driving conditions did not allow before.

  • 2017 KIA Niro 2 1.6 petrol Hybrid


Offline Craig

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It is a common misconception that running at 60 mph puts off the need for a regen.

It is just not true.

The faster you go - the more fuel you use and the more soot you create  - thus the faster the DPF gets loaded.

This misconception arises because the manual tells you that if the warning light comes on to tell you the DPF is loaded - go for a fast long drive to correct it. All this does is give the DPF the opportunity to regenerate that your previous driving conditions did not allow before.

Good information. I'm really not sure what's going on then though.
  • 2010 i30 1.6 CRDi comfort auto (pre facelift) & 2017 Hyundai Ioniq hybrid


Offline Dazzler

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It is a common misconception that running at 60 mph puts off the need for a regen.

It is just not true.

The faster you go - the more fuel you use and the more soot you create  - thus the faster the DPF gets loaded.

This misconception arises because the manual tells you that if the warning light comes on to tell you the DPF is loaded - go for a fast long drive to correct it. All this does is give the DPF the opportunity to regenerate that your previous driving conditions did not allow before.

Good information. I'm really not sure what's going on then though.

We have specialists on here for everything! Alan is our DPF and Tyre noise specialist...  :D

I would be just monitoring it over the next couple of weeks as you can't take too much notice of a short term hiccup. :cool:
  • 2021 MG PHEV ( had 4 x i30 plus a Getz an Elantra and a Tucson)


Offline Asterix

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I've had this happen twice in the 120.000 km I've had the car. Both times it was like you say, it felt like the regeneration never ends.

I try to run the car at higher revs, ca 2500 for as long as possible, don't know if it helps, but anyway....

Don't worry, it will end and suddenly everything is just fine again....  :razz:  I've absolutely no idea why this happens but as it seems to correct itself I wont spend time or money to have the car tested.
  • i40 CRDi 100 kW 2013


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