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Diesel Particulte Filters (DPF) and Rising Oil Levels - The UK Government Demonstrates the Law of Unintended Consequences

14th Jun 2010, 23:27:43

By James Stocks

The Sociologist Robert K. Merton observed that in the field of human activity, things do not go as planned and strange paradoxes may be seen. In an attempt to be 'green', the UK government has given us a perfect case study. By mandating the use of biodiesel, it has created a huge maintenance headache for motorists and perhaps increased environmental pollution. In some cases, driver safety has been put at risk.

In order to meet the Euro IV emission regulations introduced in 2005, vehicle manufacturers began routinely fitting Diesel Particulate Filters (DPF) to their diesel engined vehicles. The DPF's purpose is to filter engine exhaust gasses in order to reduce the amount of soot particles emitted into the atmosphere.

The use of DPFs prompted some complaints. Some owners complained that upon trading in a pre-DPF model for a DPF equipped vehicle, average fuel consumption fell by several MPG. Other owners fell victim to expensive repair bills because they were not using the vehicle 'correctly', that is to say the vehicle was being used for too many short journeys causing the DPF to become clogged with soot. A small reduction in fuel economy and an occasional trip to the dealer for a small number of owners is surely a small price to pay in order to save the environment, but this is only the first phase of the problem.

DPFs can only operate properly when the engine's exhaust gas reaches a temperature of 600°C or more, since it is only at this temperature that the diesel particulate matter caught by the filter will combust. If the vehicle is driven for extended periods without the exhaust gas reaching this temperature, the filter would become clogged with soot. To overcome this limitation, vehicle manufacturers use a process called 'regeneration' to clear the excess material from the DPF. Usually, regeneration involves injecting diesel during the exhaust stroke, this diesel trickles down the exhaust pipe and increases the gas temperature in the DPF. Some of this diesel does, however, find its way past the pistons and accumulates in the sump, diluting engine oil. Thankfully, this diesel is volatile and will evaporate off over time. This arrangement worked fine until the government got involved again.

All diesel fuel purchased from a filling station forecourt has to comply with the DIN EN 590 standard. In 2009 the UK government decided to fiddle about with EN 590, specifying that from February 2010 onwards all diesel fuel would be required to contain a minimum of 7% fatty acid methyl ester (FAME), a biodiesel refined from vegetable oils. The government knew that this would cause problems with some vehicles, and that fuel retailers would be required to prominently display a notice at the point of sale warning motorists that the biodiesel tainted fuel may not be suitable for their vehicle. So the government changed the law:

"Article 3(5) of Directive 2003/30/EC requires "specific labelling" on fuel pumps dispensing petrol or diesel containing more than 5% bioethanol or biodiesel by volume. This is transposed in the UK by means of the 2004 Regulations which require retailers to label pumps dispensing such fuels with the following text:

"Not suitable for all vehicles: consult vehicle manufacturer before use."

This text reflects the fact that, until recently, most vehicle manufacturers only warranted their vehicles to run on blends of up to 5% biofuel content.

On 1st July 2009 an amendment to the British Standard for diesel (BS EN 590) was published increasing the biodiesel content of diesel allowed by the standard to 7% by volume. This was in response to revised advice from the automotive industry on the biodiesel percentage with which normal diesel vehicles are compatible. Directive 2009/30/EC amending the Fuel Quality Directive 98/70/EC also explicitly permits up to 7% biodiesel content in diesel for the same reasons. Further regulations are being prepared to amend the Motor Fuel (Composition and Content) Regulations 1999 to reflect this and other changes to fuel specifications to accord with the amendments to Directive 98/70/EC."

As surely as night follows day, problems occurred. A moment ago, I said that some diesel used in DPF regeneration can dilute the engine oil, but will evaporate away over time. Biodiesel turns out to be less volatile than petrochemical diesel, so it sets up a permanent home in the sump. Over time this causes the engine oil level to steadily rise. In some cases, the oil level has risen so high that it begins to enter the combustion chamber, causing the engine to run on its own oil and an uncommanded increase in engine RPM. In some cases, this increase in RPM has been so severe that it has caused a runaway situation. Here is an account of a Fiat 500 owner on Fiat's own web site, detailing how their engine was completely destroyed by oil contamination

"My husband was driving the car home when it started accelerating and masses of smoke began pouring out of it (filling the cabin too). He pulled into a layby and the engine was over-revving madly - didn't stop even when he pulled the key out of the ignition. It was a very scary experience."

A Volvo C30 owner relates his own tale:

"I had owned my D5 for about eight months before one day it nearly sent me into orbit by itself while accellerating[sic] on the motorway. Basically the oil level had risen so much that oil was pushed somehow into the engine and burnt like fuel. The car went flat out while at the same time billowing blue smoke from the exhaust. Scary to say the least."

Other owners are, through proper maintenance, noticing the problem before it destroys their engine, such as this unfortunate chap who is having to change the oil in his Honda Civic every other month.

...I could go on. My own Volvo V50 is busily filling its sump such that I have to visit the dealer every 4,000 miles or so to have them drain off the excess oil and diesel mixture. What is the environmental impact of all this wasted diesel, extra waste motor oil, trips to the dealer and ruined engines? I bet it's more that the meagre amount saved by adding a bit of FAME to our diesel.

Update 01/01/2011

I stopped using supermarket diesel a few months ago. Except for a few trips where it has not been readily available, I am exclusively using Shell brand diesel (the 'ordinary' stuff, not V-Power) wherever possible. This seems to have brought the situation under control, since I have now covered over 10,000 miles without the oil level rising or having an oil change.

The extra cost of about 1p per litre over supermarket fuel has been worth it, not only because I don't need to get the oil changed but because I am actually acheiving a 1-2 MPG improvement in my fuel economy.

Update 01/07/2012

The problem has returned! The familiar 'Engine system service required' warning message appeared during my morning commute on Friday. My Volvo dealer was efficient as usual and was able to examine the car on Saturday morning. The mechanic drained off 750ml of oil/diesel from the sump and reset the warning light. As it was less than one litre, I elected not to have the oil changed on this occasion. The car was last serviced in late January, so I am hoping it will make it until January 2013 before it fills up again.

What's changed? As far as I know: nothing. I still regularly fill up at the same two Shell fuel filling stations, my commute is the same, my annual mileage is the same.

"Interestingly", I learned that a Volvo dealership can measure the oil level much more accurately than the dipstick will allow. A Volvo technician can connect the vehicle to their diagnostic computer, run a test, and use the engine's sensors to determine the precise volume of oil present in the engine. I think I may ask them to do this once or twice per year in between the one year/20,000 mile regular services. At least this way, I may be able to keep the situation under control, in so far as the warning light might not come on unexpectedly at inconvienient times.

Final update 01/06/2014

I never did solve this problem and I have now sold the car. 95,000 miles later I was still having warning lights in relation rising oil level problems, the most recent being in December 2013.

Some people I've spoken to speculated that there may have been another undiagnosed fault that was contributing to the problem - perhaps a dribbling fuel injector or swirl flaps not operating properly causing additional excess unburnt diesel to be present in the engine. It's certainly true that not everyone experiences this problem.

Lessons learned: If I was looking to buy a diesel car, I would choose one that was either old enough that it was not fitted with a DPF (although you'd be looking at nearly 10 year old cars by now) or new enough that it was manufactured a reasonable time after the 2009 changes to both the law and diesel formulations (and therefore should be able to cope with FAME). If covering less than 10,000 miles per year, or if many short journeys will be made, consider carefully whether diesel is the right choice for you; a petrol car may be more reliable and no more expensive.

3 Archived Comments

3rd Aug 2010, 14:08:17 by mazdacampaign
Is there a way i can find the writer of this article?



12th Nov 2010, 20:02:18 by robmar0se
My Mazda 3 2.0D also suffered from this problem. Annoying this is that Mazda rejected the warranty claim, notwithstanding a DPF update would have identified the problem earlier, and saved me a load of dosh.

12th Nov 2010, 20:19:12 by stocksy
Mazda seem to have the worst record on this. They're not recalling cars and they are blaming customers when engines blow up and shit gets real. Sounds like a make to avoid if shopping for a diesel.

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