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Are DPF's and EGR's Good?

Modern diesels are a wonderous engine. Tonnes of torque available almost as soon as you put your foot down, incredible fuel economy and great reliability makes the modern diesel the engine of choice for many car buyers. But, if you remember the old diesels of the automotive and transport industries as dirty, sooty and pollution generating workhorses, you might be wondering what exactly happened to make diesels so much more desirable.

Even though we might not have experienced it locally, diesel cars have been a popular option throughout Europe all the way back to the original VW Golf (and even before).

These old diesels often fell into the same bracket as old transport engines in being noisy and kind of dirty but, they were well known for reliability and got much better fuel economy than their petrol counterparts making them a popular option.

However, while noise is a big reason diesels weren't popular, the real issue has always been how much pollution they produce. Pollution that bought about the introduction of both the EGR and DPF (along with some other systems for another time).

The strange thing about diesel as a fuel is just how resistant it is to burning. As it goes, it’s actually fairly hard to make anything that’s diesel ignite efficiently. On top of this, partially burnt diesel produces a high amount of NOx pollution, one of the worst greenhouse gasses and the reason for the sooty exhaust seen in a lot of old diesels.

The best way to combat NOx emissions is to get diesel to burn perfectly however, with the constantly changing loads and RPM’s of a car, it’s hard to ensure that perfect burning occurs.

This is where the DPF and EGR come in. A DPF (or diesel particulate filter) is an exhaust filter that catches poorly burnt NOx emissions and stores them until the vehicle reaches a hot enough running temperature to burn them in a way that doesn’t harm the environment as much.

The EGR (exhaust gas recirculation) on the other hand is a system that uses a small valve on the exhaust to redirect a small amount of exhaust through the engine to reburn, helping to greatly reduce the NOx particles overall.

So are they any good?

It all depends on who you ask. A common complaint of the DPF’s and EGR’s is that they can easily become clogged with NOx soot and that they create another repair item for the owner of the vehicle. Additionally, the EGR in particular is often noted as causing carbon build ups on the intake side of the engine which can reduce power and cause issues over time.

However, most of these complaints really come from vehicle owners that just aren’t using their diesel engine how it was intended. The best thing for a diesel has always been running for long periods of time at moderate to heavy loads, which is also the exact conditions needed for these systems to get hot enough to work efficiently.

With so many diesels being used specifically to take the kids to school and to go on the beach once a year, it’s kind of easy to see why these systems have become a common failing point. However, in our mind, they’re worth their weight in gold.


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