Dpf
 

I bought a 58 plated V70 estate back in January & at the same time as MOT became due this month I got a "book maintenance" message so got my local small friendly garage to do both. During discussions about the car in general my local mechanic suggested that I should take it for a blast at high speed once a week to get temp up such that dpf will regenerate. This seems to agree in general with the handbook, but mechanic also advised that I should run fuel down to warning light before I re-fuel as this will help with dpf regeneration. The handbook maked no mention of this. Has anyone else heard of this strange idea? (I normally re-fuel at quarter tank).

The amount of fuel in the tank should have no bearing on the car's ability to carry out a regen and in any case I would never want to run the tank that low..

Doing a long enough journey every now and again ( high speed has nothing to do with it )certainly will though as it will allow the DPF to carry out the regen successfully if required.

There's either diesel getting to the engine or not.... that theory makes no sense whatsoever.

That mechanic seems to know nothing about regeneration.

It doesn't help driving the car fast once a week. Regeneration works better if you drive fast, but it doesn't start unless it's considered necessary by the car. Thus driving fast now and then of course increases the probability that regeneration is needed when you actually drive fast, but it could just as well be that driving fast fills the filter quicker, and the car then, at some less suitable time, finds it necessary to clean the filter.

One could imagine that regeneration doesn't start if the fuel level is very low. Just like the engine heater doesn't run if you are low on fuel. The latter is true, but the first I don't know about. Anyway, it's at least the opposite of what the mechanic said, i.e. that having a full tank increases the probability that regeneration occurs when actually needed.

My thoughts exactly I've never run a tank on any car that low as it increases the chance of stirring & sucking up sludge from the bottom of the tank

The regeneration process requires the car to be travelling at a constant speed in the mid range and for the engine to have reached its standard operating temperature. If the DPF has filled with soot, the back pressure sensor will register and trigger the regeneration. High speed is not required and while the regeneration would function at high speed, it would be more difficult to maintain a constant high speed than a constant mid range speed.

No, it does not at all require the car to travel with constant speed. But a higher engine load in general is beneficiary, since then the exhaust from the engine into the DPF is warmer, and that improves the soot incineration.
Going slowly, stopping with the engine idling - that's the worst condition.

But going up and down in speed, from midrange to high, is no problem at all. On the contrary, it probably involves higher load during acceleration, and that accelerates (!) the cleaning process.

Towing a caravan improves filter cleaning quite a lot. But it also fills the filter faster, so there's probably no net gain.

If the engine coolant hasn't reached normal temperature, around 88°C, the cleaning process doesn't start at all.

In cars where you can't see in the display that regeneration is active, the most obvious sign is that consumption doesn't display 0.0 l/100 km when you are coasting.

No it doesn't... Fuel is always drawn from the bottom of the tank, whatever the level. I guess there's an argument about lighter-than-fuel debris floating on top that may get closer to the outlet pipe as the fuel level drops, but you'd have to be practically empty before that was a problem.

There's an issue of condensation forming at less than a quarter full though.

There's always an issue of condensation in the part of the tank where there's no fuel. It doesn't start when it's a quarter full, it starts when it's not full. But it gets worse and worse, the less fuel you have in the tank.

I ran my 2007/8 V70 D5 for years and always used two stroke oil in the fuel and never had any problems with DPF regeneration inspite of doing a lot of short runs . Regeneration is only noticeable by a Hot smell when you get out of the car but never even noticed that as two stroke raises the temp of the exhaust gas and burns the particles . I now use it in the fuel of my Jaguar for the past 3 1/2 years without problem . If you do try it use s goo quality ordinary mineral based low ashself mix oil at 200: 1 ratio about 300ml to a tank. I use Carlube two stroke available from Morrisons . You will notice engine runs quieter , smoother and picks up a bit quicker .