It's official! Petrols are now cheaper to run than diesels!!!!!

Trebor16

Biglad wrote: »

It's not an urban myth actually as the DMF on a diesel is under much more 'stress' than a petrol due to the extra vibration and torque.

That's why they go wrong more often in diesels.

So where is the proof that DMF's do go wrong on diesels?

andygb

I am now seriously considering a diesel, and test drove a really nice Skoda Octavia 1.9 at the weekend. The owner drove it a short distance and then swapped over and let me drive on a good selection of roads. I thought the car was nice and smooth, pulled well, and the noise (diesel engine) was not intrusive at the speed limit.
When we got out, the missus commented that the owner's driving seemed to be very uneven, slipping the clutch too much, very jerky, yet when I drove the car (first diesel I have driven I think) it was very smooth.
The only reason I am posting this, is to question - "what is the correct driving style for a diesel?", and how do you protect the clutch by driving correctly in a DMF car?
I am on the verge of buying this car, but only if I can get it at the right price, in order to factor in a clutch/DMF change if it needs it.

Nearly_Old

andygb wrote: »

The only reason I am posting this, is to question - "what is the correct driving style for a diesel?", and how do you protect the clutch by driving correctly in a DMF car?
I am on the verge of buying this car, but only if I can get it at the right price, in order to factor in a clutch/DMF change if it needs it.

In researching last night to try and find an answer to the question asked by Trebor16 (I couldn't find any proof) I came across a few articles by engineers, service managers, etc. Their comments included:

Up to 70% of DMF failures are due to driving style / technique.

The issues with diesels include starting and stopping the engine and high low end torque. There is a higher shcok loading when a diesel is started and when it is switched off and therefore the advice repeated on many technical forums is to disengage the clutch before starting and turning off. I know that my diesels have all stopped with quite a judder that if the clutch is engaged will be transmitted through the DMF.

The other one highlighted was abuse of the low end torque; e.g. just lifting off the brakes in stop/start traffic and not using the accelerator; accelerating from 30 to 70 in 5th gear just using the torque. Again at low revs and high torque a diesel engine produces a higher shock loading that can (will) cause wear on the DMF. The concensus appears to be to drive a diesel in the same way you would a petrol when accelerating to ensure that there is a balance between torque and power before changing gear. There are cases on some forums of particular problems (early Mondeos and Transits) but there appears to be an element of design in these failures. There are also owners reporting 150k+ on their DMFs so IMHO its mainly about how you treat it that will determine how long it lasts.

andygb

Nearly_Old wrote: »

In researching last night to try and find an answer to the question asked by Trebor16 (I couldn't find any proof) I came across a few articles by engineers, service managers, etc. Their comments included:

Up to 70% of DMF failures are due to driving style / technique.

The issues with diesels include starting and stopping the engine and high low end torque. There is a higher shcok loading when a diesel is started and when it is switched off and therefore the advice repeated on many technical forums is to disengage the clutch before starting and turning off. I know that my diesels have all stopped with quite a judder that if the clutch is engaged will be transmitted through the DMF.

The other one highlighted was abuse of the low end torque; e.g. just lifting off the brakes in stop/start traffic and not using the accelerator; accelerating from 30 to 70 in 5th gear just using the torque. Again at low revs and high torque a diesel engine produces a higher shock loading that can (will) cause wear on the DMF. The concensus appears to be to drive a diesel in the same way you would a petrol when accelerating to ensure that there is a balance between torque and power before changing gear. There are cases on some forums of particular problems (early Mondeos and Transits) but there appears to be an element of design in these failures. There are also owners reporting 150k+ on their DMFs so IMHO its mainly about how you treat it that will determine how long it lasts.

Cheers for that. I reckon that I was driving it more like a petrol car - light, accurate lift of the clutch (not long and "draggy"), and then give it the beans - accelerate through the gears.
One plus point, is seeing how many taxi drivers use diesel Octavias around my way (this one is not an ex taxi, as I have seen the MOTs and servixce history), so they cannot be all that unreliable.

grizzly1911

andygb wrote: »

The only reason I am posting this, is to question - "what is the correct driving style for a diesel?"
.

Have had several diesels with no problems. Find that they don't require so many revs to get them off the mark and they tend to operate best when you use the torque rather than rev hard.

Accep the point from nearly old of not labouring the engine, but most will happily run from 1500 rpm, with max torque around 2000 revs. I rarely exceed 2500/3000 rev (through the lower gears) even in our 1.3TDi and most expire by 4000 (little advantage in exceeding) anyway.

Whilst the 1.9tdi is a robust/economical (and extremely quick in some guises) it isn't the smoothest IME.

My first diesel was a1.8 indirect Ford lump (non turbo) and whilst it was agricultural by modern standards it had a smooth drive train and I doubt that they had ever heard of DMFs then.

andygb

grizzly1911 wrote: »

Have had several diesels with no problems. Find that they don't require so many revs to get them off the mark and they tend to operate best when you use the torque rather than rev hard.

Accep the point from nearly old of not labouring the engine, but most will happily run from 1500 rpm, with max torque around 2000 revs. I rarely exceed 2500/3000 rev (through the lower gears) even in our 1.3TDi and most expire by 4000 (little advantage in exceeding) anyway.

Whilst the 1.9tdi is a robust/economical (and extremely quick in some guises) it isn't the smoothest IME.

My first diesel was a1.8 indirect Ford lump (non turbo) and whilst it was agricultural by modern standards it had a smooth drive train and I doubt that DMF.

I found that with pulling away - a really easy smooth operation.
I may have to moderate my "thirst for revs", because I think that I took it up to 4000 in 2nd and 3rd, although it did seem very willing:D
Not a hint of clutch slip either, so what should I look for as regards DMF problems, apart from knocking/clonking noises. Does the DMF fail suddenly leaving you without any drive, or is it obvious and happens over a period of time?

grizzly1911

andygb wrote: »

I found that with pulling away - a really easy smooth operation.
I may have to moderate my "thirst for revs", because I think that I took it up to 4000 in 2nd and 3rd, although it did seem very willing:D
Not a hint of clutch slip either, so what should I look for as regards DMF problems, apart from knocking/clonking noises. Does the DMF fail suddenly leaving you without any drive, or is it obvious and happens over a period of time?

They will rev, more so when the turbo kicks in, they just go past the point of delivering anything useful in the higher ranges..

Never experienced DMF failure so I will leave that to the doomsayers.