What causes MPG to decline over time?

mikeysthoughts

I see, thanks. Then if people follow the instructions there's generally not an issue?

There are loads of ICE car components which need major servicing after 60k-ish miles; timing belts, clutches, etc. Especially if the manufacturers recommendations aren't followed. I remember turbos in particular used to require spooling up regularly to prevent seizure.

Will be interesting to see what the Australian class action outcome is.

imightbewrong

The problem is there is no way of knowing really the state of the DPF or if a long journey is due or if the long journey was long enough.  It's not as simple as following a servicing schedule.

I'm sure there is a 'scandal' lurking in there somewhere.

mikeysthoughts

You've reminded me of my dad who used to moan about every single clutch he ever had failing after about 40k miles because "they're manufacturered badly"

He refused to listen to anyone pointing out that he rested his foot on the pedal and so it was causing premature wear. "I've always driven like this and it's never been a problem" was his retort.

gizlaroc

No offence meant here, but of course a new DPF will fix your issues, however, you need to find out why it was getting blocked up.

Think of it like a blocked drain, your pour fat in it, it gets blocked.
Sink doesn't drain.

You're options....


1. Clean the fat out every few months and carry on pouring fat in.

2. Replace the drain every few months and carry on pouring fat in.

3. Clean it out and stop pouring fat in.


You have chosen option 2. It will work, but it will be expensive.


Without finding out why your DPF is getting blocked you will be needing a new one again in 6 months or so.

imightbewrong

No offence taken.  I don't think it's really an 'of course a new DPF will fix it' - there were loads of options above for this poor MPG, none of which were related to the DPF, and which presumably have now been elimninated, unless they themselves can break the DPF.  So the question is whether we have fixed the cause or the symptom.

Not sure what more we can do here except stick to the DPF driving rules and monitor it.  If we need a new DPF in six months then VW will have some questions to answer.

Trollslayer

Hence the long run (40 minutes) today, I have made one long trip this year so worth doing.

gizlaroc

Well, I asked you a few basic questions which are the normal causes of low MPG and blocked DPFs and you didn't reply.

These are the basics, most MPG and Engine Management Lights on the dash can be worked out pretty easily, and the usual fixes are normally pretty cheap.
However, you will not get most garages these days, and certainly not main dealers, to actually diagnose the problem.
They will plug the computer in, see what is showing as faulty and replace it.

The problem with that with many things these days, DPF an excellent example, is they don't look for the cause.

Did you check your thermostats? Are they getting to 93ºc within 10 miles and staying there rock solid no matter what?

Did the garage check the EGR valve positions and make sure they are opening and closing 100%?

Same with the swirflaps on the manifold?

Are the O2 sensors giving the correct readings?

These are all things you can check with car readings or with a scanner plugged in for 3 minutes, and all things that are known to cause the issues you have had.

Thermostat is the big one, serviceable part, that needs to be working for a regen to start. I have seen so many cars where BMW, VW, Audi etc. have said "Needs a new DPF." be sorted with a £40 thermostat fitted, within miles the car can regen and DPF warnings are gone.

Remember, the car over fuels by as much as 40% when it is trying to regen, and if it can't regen it will constantly try and constantly over fuel.


I have yet to see a car that needs a new DPF, it is always something else, and that something else can be found quite easily if those looking can be bothered.

Trollslayer

Have to say I am lucky, the place I use is run by a couple of enthusiasts who could have retired a while back but it is their thing.
First time I went there they had an immaculate E-type on the ramps. In red of course.

imightbewrong

Thanks for the detail.

I wouldn't know where to start doing any of that. We've been discussing this issue for a long time with VW and our local guy - they've tried a lot of things before the dpf change which they were reluctant to do. I have to assume they have done all the sensible mechanic things before this.

gizlaroc

I always buy a scanner, the amount of money that has saved me over the years has been unreal.

They are getting so cheap now as well.