Diesel Particulate Filter

[tetsudofan]

Have been reading this with interest but must admit that I don't take much interest in what is under the bonnet.

 

Since 2005 I've had three diesels (Mercedes A, B and since last March a GLA - supposedly the first one on the road in the UK) but have never been aware of a dpf warning light on the car. Looking through the GLA manual I can't find mention of one.

 

Know it's a stupid question but do all diesels have a dpf?

 

Looking at the technical data for the GLA its got an EU6 diesel with CO2 emissions of 119 g/km. Compared with my A & B Class the GLA has much better fuel consumption figures - when I went up to Telford last year for the O-Gauge meet managed to get 60mpg which quite surprised me - much better consumption than from the A & B with a slightly bigger engine on the GLA.

 

Keith

[28XX]

I concur with all who advocate the new small but powerful petrol engines.  My Skoda Octavia estate is a 1.2 litre TSI, bought in a hurry last August.  It is 103bhp, like a 1980 Cortina 2000 and frankly it's at least as fast, but quiet and flexible as well.  Although a 6 speed, I tend to miss out 3rd and 5th unless I'm in a real hurry, such is the breadth of the power band.

 

Drefus, you are in a quandry here.  Your budget is too high to be interested in a pre DPF diesel, but too low to afford a TSI or similar.

[BrushVeteran]

Any engine these days requires to get hot enough to burn off the particulates, whether it be petrol or diesel. Under normal use or even short journeys the CAT or paticulate filter will get hot enought to burn off the normal fuel residues associated with an engine that is in good condition. Good condition means clean air filter and reasonably clean engine oil. The problem arises however when the CAT or particulate filter becomes clogged with impuities such as unburnt engine oil or fuel. This is usually caused by worn piston rings that allow engine oil into the combustion sytem and thus fails to fully combust. A knackered engine in either a petrol or diesel powered vehicle will fail its MOT each year no matter how many times you change the CAT or pariculate filter. This is because there is so much residue and the engine requires a higher temperature to burn these off if it can. So if you regularly have to put engine oil in your vehicle and it is not leaking then you stand more chance of your CAT or particulate filter becoming clogged. When going for an MOT test it is always best to give the engine a good thrash to get it hot so that when tested the temperature is correct for the test procedure. 

A couple of years ago my wife took her car, a Rover 45 diesel, to the garage for test.......about 400 yards away.........and guess what it failed on emissions. They failed to get the engine up to working temperature..which they are supposed to do.. and wanted to replace the CAT at £500.  We took it to another garage fifteen miles away and there was not a problem with the emissions. It sails through the test each year but I do change the oil, fuel and air filter annually........even though it only does less than 5K miles per year.

 

I don't think that there is much to choose between performance on petrol or diesel powered vehicles these days but my experience in working with buses for the last 40 years has taught me a great deal of respect in what you can save if you drive a diesel correctly.  I think its a case of you pay your money..............................!

[Claude_Dreyfus]

Some very interesting reading here...thanks all for the input thus far. Based on comments here, recommendations from othesr I know and a trawl through various websites, maybe a diesel is not the best option for me. Finding a petrol XC70 may well be virtually impossible, but petrol V70s are out there... 

[briantwigley]

I have a diesel - 63 plate Golf and I've never had any trouble with the DPF. I drive 22 miles each way to work and back, and do about 18k miles a year. 

 

I drive a van for work around the town and about once a month I get a filter warning and have to take it home with me to clear it out. If you're doing long journeys each way it should be fine.

 

I have also driven one of the 1.0 EcoBoost Fiestas and I found it had more torque than my 1.6 diesel, and I would seriously consider getting one, if Fords were better than my VW. 

 

I only got the diesel for the good MPG and free tax. 

 

Ryan

[jjb1970]

The road tax on the Golf 1.4TSI 140PS with a DSG box is only £20 a year and when I've used it to go to work in Southampton from time to time Iget almost 60mpg average door to door. That is pretty impressive for a Golf sized car with a petrol engine and auto box which can do 0 - 60 in 8 and a bit seconds.

[Mallard60022]

Only one thing from me. Beware of ex diesels that have been mini/cabs/taxis! How do I know this...............? Cost/lost me about £4K over 2 years!

Phil

[MJI]

I remember many years ago being told that the future was in 330cc cylinders, particularly 1 litre triples, and now everyone is making them. The important thing in combustion is getting enough air in. With forced induction and variable valve timing, the swept volume is not as important as it was, despite the US mantra "you can't beat cubes".  Accurate petrol injection is now cheap and universal, so really the trick is to make the tiddly engines strong enough for the high pressures generated. 

I think the most powerful F1 engines were the 1.5 litre turbo cars which could produce 1000 HP in qualifying. Some spectacular failures though!

 

Ed

 

1100bhp in qualifying

[MJI]

Worth a read, this sort of thing will only increase.

 

http://www.dailymail.co.uk/news/article-2913674/Council-charge-diesel-car-drivers-extra-100-park-outside-homes.html

 

I personally would not touch a modern diesel unless I did very high mileages, which I don't. It's not just DPF's, also injection systems, EGR valves etc.

 

The days of cheap diesel motoring (v.s. petrol)are coming to an end.

 

Brit15

 

I have recently bought my first Diesel (couldn't find a new enough petrol).

 

EGR is in the garage, the intake manifold was full of gunge, cat will be following this year, other owners reckon decatting is worth 10% more mpg.

 

It drives OK, economy is not great but better than the petrol would have been, and little performance difference (has mine been remapped?)

 

Newer Diesels with DPF, unremovable EGR, very high states of tune worry me. Mine is a 2.5 five with unit injectors and sounds like a truck, however my annual mileage is around 10,000.

 

I would have been happy with the V8 prefereably on LPG

[Spannerman]

Hi

 

I have an XC90 D5 with dpf and do get an occasional warning light and "engine system service required "message which is linked to the dpf system.

 

My understanding is that when the Dpf starts a filter regen, injecting diesel into the system to burn hotter and clear any deposits. Should it not be able to complete the cycle the unused diesel is dumped back into the oil sump(diesel being a lubricant this is not a problem).

 

This causes 2 problems.

 

1. The oil level rises - the fill level being 2/3Rd up the dip stick not to the top marking- which can require some draining off.

 

2. If the car is used only for short journey's a full regen will not take place unless the car is taken for a good run.

 

The warning light on my car clears as soon as a regen has been completed.

 

So far the dpf hasn't really caused us any worries and with the type of driving you describe I wouldn't hAve thought you'd get to much trouble.

 

Hope this is of some use.

 

ATB

 

Nik

[JeremyC]

 Should it not be able to complete the cycle the unused diesel is dumped back into the oil sump(diesel being a lubricant this is not a problem).

 

I find that a surprising statement. To quote from a lubricating oil analysis report on one of the generator engines of the ship I work on:

"The analysis results, based on the tests performed, indicate that it [the lubricating oil] is unsuitable for continued use, due to the low flashpoint which is indicative of fuel contamination."

 

The fuel we use is Marine Gas Oil which is similar to 'Red Diesel'.

 

If your engine sump is filling up with fuel I think you've a problem.

[Spannerman]

I think the AA explain it better than I can. And as you rightly say the oil quality does deteriorate.

 

 

http://www.theaa.com/motoring_advice/fuels-and-environment/diesel-particulate-filters.html

 

Atb

 

Nik

[jjb1970]

The real issue with fuel dilution of lube oil is the drop in viscosity which affects lubrication. There is also the affect on flash point. Lube oils are loaded up with various cleaning, anti-oxidant etc additives which will be affected. In short fuel dilution is generally a major problem for lubricating oils.

[brianthesnail96]

Effectively you get a very late injection, after any useful work has been completed and immediately prior to the exhaust valve opening. Assuming there is still sufficient heat in the engine for this injection to fully combust this will then heat the DPF enough for it to burn off the crud. If you don't have enough heat in the engine, I..e. slow down after the process has started, until the ECU registers that it's no longer hot enough for complete combustion, you'll get fuel condensing on the bores which will have a "washing" effect and end up in the sump. This should only be fairly small quantities, unless you never actually let it complete a cycle and it keeps trying and failing.

 

Part of the reason for the wholesale adoption of common rail technology is that it gives you the flexibility to pull tricks like this, and similar late injection techniques for maintaining catalytic converters at optimum temperatures as well.

 

Although diesel has fairly good lubricating properties (high pressure fuel pumps etc are self lubricating), it's nowhere near good enough for engine components due to it's low viscosity (it falls off the things you want to lubricate instead of clinging on, basically) and as such significant lube oil dilution is a Bad Thing.

 

As said previously, the solution is easy- instead of relying for the car to do it for you, take it for a damn good thrashing every now and again! Occasional runs at high (within the allowed range!) revs and getting a lot of heat in the system will help reduce carbon build up in the combustion chambers & exhaust, and the higher fuel flows will help keep the injectors and fuel pumps clean too, as well as allowing DPF regeneration. Obviously driving everywhere flat out all the time will lead to premature wear but engines are designed to use the full RPM range specified and you won't do any harm by allowing it to do so every once in a while- there does seem to be a mentality that to ensure a long engine life you should drive like a granny everywhere and that simply isn't the case, even more so with modern engines which have considerably more advanced lubrication systems (and oils) than what we had in the 60's and 70's.  

[MJI]

Well this is interesting, it also seems to be why unit injectors in cars seems to have been abandoned.

 

Looks like the best bet is an older car or a petrol.

 

I never regularly go near any really big cities nearest would be NEC.

 

My car takes 8 miles to get fully warm my commute is 12, my old car was quicker to warm up.

[brianthesnail96]

Pretty much! There are a few advantages to common rail (it's quieter for one, and theoretically slightly cheaper as you can get away with fewer pumping elements), but the main reason is it's flexibility for meeting emissions requirements- you can get an earlier pre injection and a later post as required as you don't have to wait for the pump to be "on cam". You can also do multiple injections within a single combustion event, to try and get as much fuel to burn as possible!

 

For the uninitiated, the simple analogy is it's the difference between taking water from a reservoir against from a stream- with common rail you don't have to wait until it rains hard...

 

This also explains why there's often a fuel consumption hit for engines with lots of aftertreatment, as you end up injecting fuel at various times where it performs little or no useful work in terms of making the whizzy bits go round, instead providing energy to optimise the aftertreatments. This is offset to an extent by the more complete combustion of the fuel used in the main injection event(s).

 

Unit injectors are not completely dead- for example some of the EU6 Volvo truck range use unit injectors to pressure a common rail as result of wanting to fit a common rail system to engine architecture designed for unit injectors.  

 

It's generally reckoned that Euro 6 is about as far as we can sensibly go at the moment for NOx and particulates (not unreasonably, given that in heavily polluted areas it's perfectly possible for the exhaust of a EU6 vehicle to be cleaner than the air going in) and that Euro 7 will focus on reducing fuel consumption- which could lead to some interesting vehicle designs as aerodynamics will start to play and even bigger role.

[cheesysmith]

The new euro6 regs have already started having a interesting effect on bus engines, in that the engines are getting smaller to more easliy meet the emissions standards, with quicker warm up and better part throttle fuel economy. To get the power needed, the turbos and boost pressure have gone up, but this does Lead to a potential for shorter engine life due to greater stresses involved. But when you can get a new engine for less that the cost of a full rebuild of a older engine, you can understand why.

 

For a example, in Sheffield, with it's wonderful terrain, we have gone from using busses with 12L engines to 4.7L engines.

A list of what we have used in the 14 years I have worked on them.

Dennis dominators, DD, 12L engine, lousy fuel economy and emissions, but was 20+ years old.

Volvo B10 in m and ble versions (the last of the ble's are being withdrawn). Euro 2 spec, about 6mpg.

Volvo B7l/tl, DD and singles, euro 3 spec and between 3.5 (ex London busses) and 5.5 (singles)

Volvo B9tl, DD, euro 5, 4.5 to 5.5 mpg.

Streetlite singles, euro6, about 10mpg (sometimes more), these have light weight build to reduce the mass of the bus, and have a 4.7L cummins engine match to a specific gearbox.

We have on test a new streetdecker with a 5.1l Daimler Benz engine that is doing about 7mpg.

 

As to life of the above, the dominators lasted 25 years, the B10 Volos have done 20 years(and it's only the lack of spares and age of the electrics that counts against them). The B7s require a engine rebuild every 5 to 7 years. The b9s are ok, as long as you keep on top of the emissions gear and injectors. The worst busses we have are some ex London Dennis DD with 8L engines. These engines have a lack of low down torque, which leads to camshaft wear, and results in the engine going bang (the most spectacular was one that had a leg out of bed).

[Kickstart]

not unreasonably, given that in heavily polluted areas it's perfectly possible for the exhaust of a EU6 vehicle to be cleaner than the air going in

That was claimed for London air for various petrol engines in the late 1990s.

 

All the best

 

Keith

[brianthesnail96]

Quite probable Keith. We can do it with diesel HGVs now

 

Edit- found the chart I was looking for, shows how much we've tightened up on NOx and particulates and why all these pain in the proverbial aftertreatments are needed- they don't fit them for fun!

 

[jjb1970]

Part of my job is certification of marine diesel emissions and this is actually becoming a problem for manufacturers as for some pollutants the emissions are indeed below what is being drawn in.

[Bert Cheese]

I'm on my first and hopefully last diesel (Alfa GT 1.9 JTD) despite it being the best all round choice of the model range...the future for diesels is looking rather bleak now with ever tightening emissions standards since 2009 (Euro 5) in particular.

As can be seen below though it made the most sense given the petrol line up for the same model:

Petrol versions: 1.8 TwinSpark - Getting on a bit, fine in a 155 but not enough grunt for a heavier GT, not surprisingly hard to find.

                          2.2 JTS - Awful GM derived rubbish with many problems, best avoided.

                          3.2 Busso V6 - Sublime & classic engine but expensive to run and maintain properly...18 MPG when driven as it should be.

 

My 1.9 JTD conforms to Euro 3 emissions and has had the EGR blanked as part of a remap taking it from 150 to 185 BHP with loads of extra torque while no longer rebreathing its own emissions through the inlet manifold caking it in black soot (I had this removed and internally cleaned with walnut shells through a sandblasting gun!)  Luckily I have no DPF to worry about which can cause all sorts of bother on the newer Brera 2.4 JTD's.

Still getting over 50 MPG on average though and overtaking even in 6th gear is effortless on the motorway, gets comments from strangers when filling up more than any other car I've owned too...which is nice I suppose, the red leather is a bit pimp style though!

 

Yet despite the above I sort of realised I had bought the wrong car last year when attending a car show at Beaulieu, I had polished the thing to near perfection but it still sounded like a taxi when idling, as I parked up a pair of GT 3.2L Busso V6's (best mass production V6 petrol engine ever made!)  rolled past just throbbing away at tickover so the ground resonated slightly...I looked at mine and in James May style thought "Oh cock"

 

My next car choice in a couple of years time looks like a tough one...I always knew which Alfa I wanted next from 1991 until recently but they are no longer as special as in days gone by and with no reason to buy with the heart a more sensible offering may be affected by the head...something fun and petrol powered, but what?

[Pugsley]

I'm starting to think that my current car, a Mercedes C200 CDI is going to be my last diesel car. I'm currently considering alternatives and I'm thinking about a Subaru Impreza for my next one.

[cheesysmith]

Off your next car may I suggest looking for something either stupidly small, like the little corsa company van we have at work. The thing has tiny narrow tyres and a little 1.3 diesel turbo. You have to thrash it to death to get any go out of it, cause its useless off boost, and because there is no mass to carry round, it does fly when you do. Those little tyres mean when the white stuff falls out of the sky, it can get places more expensive cars can't. Or get something with 4wd saloon car. I had a xr4x4 and remember in winter passing land rovers that were stuck in the white stuff. It may have only done 20mpg, but it never got stuck. A 4wd saloon is so much more than just winter use though. The grip and sure footed road holding it give you just have to experience to believe.

[Horsetan]

...Looks like the best bet is an older classic car ......

There, that's better. Could be VED-exempt as well....!

[Dan Griffin]

Hi all, here's an insider tip, my peugeot 407 'failed' with the dreads dpf problem. The oil for the filter is extortionatly expensive. do not buy any! My mechanic used the best quality neat diesel he could get, I think it was shell premium. Done the trick! No more problems