Diesel particulates filter clogs if low mileage?

GDB2222

We were thinking of getting a diesel car, perhaps 8 or 9 years old. We live in London and mainly do short journeys- typically 5 miles. Are we likely to have problems with the filter?

MikeJXE

I have Jaguar XE diesel. 6 years olds that I bought 3 years ago with 22.000 on the clock

I use it mainly at weekend to visit the kids 5 miles away, I also do some in the week less than 2 miles although I do do longer miles too typically 10 or so and do 6,000 per year

I have had no trouble whatsoever 

Mr.Generous

My Saab was fine when I did a few miles, and poor when I finished work and did mainly short trips. It did a regen easy enough, but what a pain and waste of fuel.

sevenhills

My 2013 Zafira has done just one regen, that I am aware of, in the past three years. I do 4,000 miles per year. I believe mine is Euro 5

baser999

My understanding is that it’s wise to give such a car a decent run every now and again to give the DPF a clean. You’ll certainly need to consider ULEZ if you’re looking at buying something older.

Bigwheels1111

GDB2222 said:

We were thinking of getting a diesel car, perhaps 8 or 9 years old. We live in London and mainly do short journeys- typically 5 miles. Are we likely to have problems with the filter?

Do you know the ULEZ is on track to expand and cover almost everywhere inside the M25.
Unless it’s a euro 6 Diesel from 2015 ish you will be charged £12.50 a day to drive.
I would go with a Toyota Hybrid.
My mate cabs his Prius in London get 55-58 mpg.

I have a euro 6 diesel, and will get an extra 4 year exemption if the euro 7 comes out and they ban euro 6
as car is registered disabled.
My next car will probably be a Toyota Corolla estate 1.8 or 2.0L petrol.
EV is not an option for me.

sevenhills

Bigwheels1111 said:

Do you know the ULEZ is on track to expand and cover almost everywhere inside the M25.
Unless it’s a euro 6 Diesel from 2015 ish you will be charged £12.50 a day to drive.
I would go with a Toyota Hybrid.
My mate cabs his Prius in London get 55-58 mpg.

I have a euro 6 diesel, and will get an extra 4 year exemption if the euro 7 comes out and they ban euro 6
as car is registered disabled.
My next car will probably be a Toyota Corolla estate 1.8 or 2.0L petrol.
EV is not an option for me.

Surely every car owner in London knows about that. I have heard about it a few times on the news.

Goudy

A DPF is designed to trap soot in the exhaust, then when it detects the filter is filling with soot it will need to actively regenerate.

This means the engine injects extra fuel on a post combustion cycle so it makes it way into the DPF unburnt which it ignites and burns the larger particles of soot to smaller particle of ash, which it can hold more of.
Even if it all works perfectly it will eventually fill with ash and require attention.

To do this it needs the right conditions, to burn the soot to ash temps have to be really high (some French cars use another fliud, EOLYS to reduce the temps needed) and if you don't quite get them you can start having trouble.

Obviously if the regen cycle doesn't start or complete because you have switched the engine off or it can't meet the right conditions, you fill the filter with soot far quicker than it would fill with ash and the car will detect excess back pressure from the filter and complain via the on board diagnostics.

Another issue if the cycle doesn't complete is the fuel that is injected post combustion.
This can seep down past the pistons and dilute the engine oil.
Not only does this alter the oil properties, but if it happens enough the oil level will rise and if the oil rises enough the engine can "run away" on it (run uncontrollably on it's own engine oil).

If you get the the point of having lots of incomplete regens, it becomes a vicious circle.
The car will try more and more to regen, injecting more and more post combustion fuel which then might not complete, exasperating the problem.

The issue with short tripping a diesel is then tend to make a bit more soot when started cold, the chances of reaching the ideal temp conditions for a regen are greatly reduced and the chances the engine might not be running long enough is also high.

Some cope with this better than others, as already mentioned there are systems that can help the regen process on some cars plus everyone's driving habits are slightly different, but short tripping one isn't ideal.

With your trips being so short, you probably aren't going to see the cost difference in fuel back any time soon either.
Diesel is far more expensive than petrol and to make that back you will need to do a lot more miles.

Some petrol cars have particulate filters but they work very differently.
For one they don't produce as much soot, plus it's a passive system.
Heat from the exhaust gas on the over run (when you take your foot off the pedal) is really really hot and it uses this to burn any soot to ash in the filter.
As there's less soot to start with and the regen is passive and happens many many times when you are driving, these tend to be far more reliable.
In fact, short tripping usually means you're on and off the pedal far more often which helps the process.

Bigwheels1111

sevenhills said:

Bigwheels1111 said:

Do you know the ULEZ is on track to expand and cover almost everywhere inside the M25.
Unless it’s a euro 6 Diesel from 2015 ish you will be charged £12.50 a day to drive.
I would go with a Toyota Hybrid.
My mate cabs his Prius in London get 55-58 mpg.

I have a euro 6 diesel, and will get an extra 4 year exemption if the euro 7 comes out and they ban euro 6
as car is registered disabled.
My next car will probably be a Toyota Corolla estate 1.8 or 2.0L petrol.
EV is not an option for me.

Surely every car owner in London knows about that. I have heard about it a few times on the news.

Why would GDB2222 want a diesel then, risk of clogged dpf and a daily charge.
It was news to me, when I found out about it a month ago.

GDB2222

What happens when the DPF is full of ash? Can it be emptied out, or do you need a new dpf?

Mr.Generous

GDB2222 said:

What happens when the DPF is full of ash? Can it be emptied out, or do you need a new dpf?

Need a new one, but sometimes they are cut out of the exhaust, stripped out completely and its welded back up - but an MOT failure if spotted. Also might fail the smoke test at MOT time. Ive also seen a video where they cut it out of the pipe, pressure washed it (unbelievable amount of crud came out) and refitted it. None of these options are cheap.

You also have the issue with EGR* valves on low mileage diesels - I owned an Astra once and had to strip and clean that twice.

*Exhaust gas recirculation - any unburnt fuel in exhaust and it goes through the engine again resulting in sooty clog up.