Buying a used car: would you buy a diesel?

pred02

Hi,
I live in South London Zone 2 and am looking to get a car. The car I was looking into is a 2015 TDI which is currently ULEZ compliant. It's a great car with good mileage etc, I am wondering if there is discussion or a risk that regulation will further change for ULEZ making this a risky purchase.
Also - this is my first time buying a 2nd hand car in the UK - sit there a good serve for doing independent checks?
Thanks,

knightstyle

Private or garage sale?  If it were me I would buy after doing usual checks and a test drive.
https://www.moneyadviceservice.org.uk/en/articles/how-to-test-drive-and-check-a-used-car

pred02

knightstyle said:

Private or garage sale?  If it were me I would buy after doing usual checks and a test drive.
https://www.moneyadviceservice.org.uk/en/articles/how-to-test-drive-and-check-a-used-car

Thanks. It's a garage sale through an independent used car dealer. Thanks for posting the article, I will read up on it.

Mutton_Geoff

I wouldn't buy a diesel car now. Especially if you live and are going to use it for (short) stop start journeys in and around London.

AdrianC

The ULEZ requires Euro6 emissions. That's the current main standard, with Euro7 not on the horizon any time soon. If it gets narrowed down any tighter than that, I suspect it'll be to restrict to only electric vehicles - but that won't be for years, since the ULEZ is currently only the congestion charge, with expansion to the circulars coming in October next year. There would have to be time for consultation.

oh_really

pred02 said:

The car I was looking into is a 2015 TDI 

Beware its due a cambelt change so factor price into your decision. I got mine done at dealer who offered a discount off retail.
https://www.volkswagen.co.uk/owners/servicing/pricing

MinuteNoodles

pred02 said:

Hi,
I live in South London Zone 2 and am looking to get a car. The car I was looking into is a 2015 TDI which is currently ULEZ compliant. It's a great car with good mileage etc, I am wondering if there is discussion or a risk that regulation will further change for ULEZ making this a risky purchase.
Also - this is my first time buying a 2nd hand car in the UK - sit there a good serve for doing independent checks?
Thanks,

Regardless of any future changes to the ULEZ...

Do not get a diesel that is post 2008 if the vast majority of your driving is urban driving. The reason for this is they're fitted with a DPF or diesel particulate filter. This traps soot that normally comes out of the exhaust of diesel cars, stores it then periodically heats it up and turns it into harmless ash which then gets ejected out of the exhaust in what is called a regeneration or regen cycle. This usually involves driving continuously for 30 minutes or more typically at speeds over 40MPH.

The problem is that the DPF has to get hot enough to do this regeneration cycle which it doesn't during urban driving. Eventually it gets clogged so much if it never gets the chance to that it needs replacing at the cost of several hundred to over a thousand pounds. 

Diesel cars pre-2008 don't have DPF filters but then they're only Euro4 compliant.

Jonesya

I've owned a couple of diesels and the engines were pretty reliable apart from the EGR needing a clean, easy on some cars but difficult and costly on others if the EGR is difficult to access. But both of these were Euro 4 or earlier so don't have a particulate filter or catalyst.

That said, I doubt I would buy another diesel because everything I hear and read about the latest models with particulate filters is that the filters and regeneration systems are prone to faults and have a limited life, so likely to require costly replacement during the life of the car. I'm sure they're fine in the first few years under warranty but they seem a gamble as a used model. 

Its only an anecdote but the people I've known with DPF problems have struggled to get an accurate diagnosis of the cause, so has needed several costly visits to garages, trying several things to fix the issue.

MinuteNoodles

Jonesya said:

That said, I doubt I would buy another diesel because everything I hear and read about the latest models with particulate filters is that the filters and regeneration systems are prone to faults and have a limited life

That's if you get the wrong type of vehicle for the types of journey you do. The life is only limited by how blocked up they get and if they're getting to do regular regenerations they shouldn't do. The lorries I drive have a DPF gauge on them to show how full they are, every one in the fleet of over 100 does night trunks of 250-450 miles and even those which have done a million km the gauge shows nothing or maybe the very slightest bit but we're talking under 10% after a million km.

My last car, a 2010 MK4 Ford Mondeo, I bought at 2 years old with 38k on the clock. I sold it to my parents last year with 155k on the clock. Still on its original DPF filter, never had a problem other than a small rubber pipe going to a sensor cracking with age which the garage changed for £5. But I hardly ever do any urban driving and my commute to work is 30 miles each way on rural A roads where only a mile or so is below 60MPH and its regularly done long journeys too. 

Nuggy96

MinuteNoodles said:

pred02 said:

Hi,
I live in South London Zone 2 and am looking to get a car. The car I was looking into is a 2015 TDI which is currently ULEZ compliant. It's a great car with good mileage etc, I am wondering if there is discussion or a risk that regulation will further change for ULEZ making this a risky purchase.
Also - this is my first time buying a 2nd hand car in the UK - sit there a good serve for doing independent checks?
Thanks,

Regardless of any future changes to the ULEZ...

Do not get a diesel that is post 2008 if the vast majority of your driving is urban driving. The reason for this is they're fitted with a DPF or diesel particulate filter. This traps soot that normally comes out of the exhaust of diesel cars, stores it then periodically heats it up and turns it into harmless ash which then gets ejected out of the exhaust in what is called a regeneration or regen cycle. This usually involves driving continuously for 30 minutes or more typically at speeds over 40MPH.

The problem is that the DPF has to get hot enough to do this regeneration cycle which it doesn't during urban driving. Eventually it gets clogged so much if it never gets the chance to that it needs replacing at the cost of several hundred to over a thousand pounds. 

Diesel cars pre-2008 don't have DPF filters but then they're only Euro4 compliant.

This is only a major issue in cars between i think 2010 and 2015 and thats because car manufacturers had no clue the issues it would cause. They put the DPF too far away from the engine so it never got hot enough. From 2015 onwards the DPF is much closer to the heat and thus the issue is more uncommon.

Jonesya

MinuteNoodles said:

Jonesya said:

That said, I doubt I would buy another diesel because everything I hear and read about the latest models with particulate filters is that the filters and regeneration systems are prone to faults and have a limited life

That's if you get the wrong type of vehicle for the types of journey you do. The life is only limited by how blocked up they get and if they're getting to do regular regenerations they shouldn't do.

Actually the issues I'd heard about were from long distance drivers, where they'd had problems with the regeneration systems because many models have active regeneration, injecting fuel to burn off the particulates in the filter which relies on various pressure sensors and controls to activate the regeneration. If you get problems with sensors, or any of the other parts in that control system then it can stop it regenerating, clogging the DPF and causing issues, putting the car into limp-home mode. I don't doubt the DPFs on long distance trucks are very reliable, but then I'd expect they're engineered for a much longer life and mileage than a typical passenger car.