*Warning… Graphic Content will shock Diesel vehicle owners!*
This is the dreaded Soot & Carbon build up in the inlet manifold of a 2007 Mitsubishi Triton!
EGR – The Ugly Truth
Every day, without fail, I get asked about EGR systems (Exhaust Gas Recirculation Devices). I’ve
heard some very creative stories that seem to stem from the world of the internet forum warriors. It
appears that everybody has completed their google degree on Emissions Control equipment on modern
Common Rail Diesel vehicles and has their own solution.
With every customer being just as confused, or misinformed as the last, I have set about writing this
article to educate you about the REAL TRUTH behind EGR systems, how they function, what exactly
they do and what side effects they can have to the service life of your rig, and how to prolong exactly
So, what is it?
First and foremost, the EGR system is a form of emissions control equipment, fitted to a modern diesel
engine from the early 2000’s onwards (in Australia). All vehicles must comply with ADRs (Australian
Design Regulations) and emission outputs are a critical part of the criteria manufactures must meet to
allow access to the Australian market. The EGR is employed to reduce the amount of NOx (Nitrogen
Oxide gases) produced by the vehicle during the combustion cycle of a Compression Ignition Engine
(Diesel). These NOx gases are harmful to our environment. The EGR’s job is to take a portion of those
spent gases, and recirculate them back through the intake side of the motor, re-introducing them to a
secondary combustion cycle to be re-burned, and broken down into smaller elements to produce a
smaller carbon footprint… A good thing for our environment, but not so healthy for our motor.
So, you might ask, if it is good for our environment, why is it not good for my motor?
Because of the characteristics of a modern Diesel engine, they often “breathe heavy” and will see what
is referred to as “Positive Crankcase Ventilation”. This is necessary because an internal combustion
engine inevitably involves a relatively small, but continual amount of “Blow-By” which occurs when
some of the gases from the combustion cycle escape past the Piston Rings and are trapped inside the
crankcase, causing a pressure build up. To regulate this pressure, a PCV (Positive Crankcase
Ventilation) Valve is used to vent the crankcase, carrying this pressure, and inevitably, a small amount
of engine oil with it back into the intake, much like the EGR does with NOx gases. Each of these
alone, taking this path, don’t cause an issue.
What Goes Wrong?
Ever spilled flour when baking cakes with Grandma as a kid? Easy to clean up, right?
Ever spilled water when baking cakes with Grandma as a kid? Also, easily cleaned up right?
But, ever combined flour and water and spilled them both together? Makes an almighty claggy mess
that is hard to clean up! The same goes for your motor when the PCV Valve and EGR System get
together and decide to have a party like two naughty kids and cause mischief without you knowing.
The combination of NOx Gases and Oil particles when they meet in the Intake Manifold and EGR
Valve, causes a claggy, sticky, build-up of Carbon that eventually solidifies over time.
It has a similar effect to Cholesterol in the arteries of a human body…eventually blood can’t flow and
the result we all know too well… heart attack, stroke, the list goes on. It is the same for your motor.
Eventually the carbon build-up becomes so severe, that the air flow that is so critical to a Diesel
motor’s operation is so far reduced that it causes rich AFRs (Air-Fuel Ratios) drastically reducing the
efficiency of the motor. Symptoms can cause the motor to run unusually hot, fuel economy going out
the window, lead the vehicle to produce a “flat spot” or “laggy” sensation during take-off, or simply just
a severe lack of power. Unfortunately, and to my astonishment, a lot of drivers don’t feel this
happening! But, to be fair, 99.99% of the time it is not due to their own fault, but due to a lack of
Left untreated, this build up eventually causes the intake to become so blocked, the inevitable heart
attack takes place, and people are left wondering why they have a 40,000km old vehicle, they have
spent upwards of the average person’s annual salary on has decided to give up the ghost and requires
a new motor. I don’t mean to alarm you, but the prime victims are tradies, and young families that use
these around town, as shopping trolleys or mum’s taxi. Reason being; an EGR Valve generally
operates at 60km/h road speed or less. The science as to why I can cover in a later article, but it
stands to reason; Tradies, mums, and daily tarmac prowlers beware! This IS happening to your rig.
What is the solution?
Well, put simply, EGR’s aren’t leaving us. They are here to stay and emissions control laws are getting
even more stringent. I have spent a fair amount of time in Europe during my career for one reason or
another, and when we see in Australian what they have there right now, most people will be left
scratching their heads. Another article for later. My suggestion is to outlay a small investment in your
rig in two areas.
●Invest in a Catch Can –
Catch Cans have been common place in motorsport for a long time. Now they should be the first,
single most affordable investment you can make to your Common Rail vehicle. It traps and separates
the oil that the PCV recirculates, preventing it from having that party with the NOx gases we touched
●Invest in a De-Soot or Carbon Clean
If you fit one of that criteria of tradie, school run mum or daily driver of any description, have your
manifold and EGR system inspected, and cleaned. There are several ways to do this, and it is FAR
cheaper than a new motor, labour and downtime is FAR less, and I guarantee you’ll thank me for your
economy improvements later. Who wants to spend money on fuel anyway? It’s already dear enough as
I hope that answers some of the myths that are floating around the forums now. If I had a dollar for
every story I’ve heard, I could’ve produced a skit to air on the nine network at prime time by now. Still
curious? Give us a call or drop us a message.