25/10/2024
EGR - The Silent Killer?
Without diving too deeply into the mechanics, let’s briefly cover what the system is and how it works. EGR stands for Exhaust Gas Recirculation. As my tech-savvy audience probably knows, this system routes some of the exhaust gas back into the engine to meet certain emission targets.
Don’t get me wrong—I’m not against cleaner air or suggesting we eliminate technology designed to achieve that. But, there’s a big "but" in this situation. Lawmakers and car manufacturers don't seem to be fully cooperating in this area. Lawmakers demand certain emission standards, and manufacturers design engines to meet them, right? Simple enough. But no, I wish it were that straightforward.
Let me explain what’s actually wrong here.
To fully understand my point, we need a deeper understanding of why the EGR system is installed and what happens during its intended operation. As you know, the EGR system routes some of the exhaust gas back to the engine’s intake to reduce emissions.
How?
In simple, non-scientific terms, the idea is to reduce oxygen levels in the combustion chamber. The EGR system does this by redirecting a predetermined portion of exhaust gases back into the intake. This way, the engine’s total gas intake volume remains the same, but since some of the intake consists of "dead air" (technically, inert gas), the oxygen content in the combustion chamber decreases.
This approach is chosen because diesel engines don’t have precise control mechanisms for intake air quantity. Yes, diesels have throttle bodies like gasoline engines, but they serve different purposes—mainly EGR flow control and engine shutdown.
Now, you might ask, why is excess air in the combustion chamber a problem? You’d be right to question this. The issue is that at certain pressures and temperatures, air breaks down and reacts with leftover combustion products to produce NOx gases. Keep in mind that air is about 80% nitrogen.
Why call this article "The Silent Killer"?
So far, we’ve only covered the principles behind the system and highlighted its advantages. But it’s not all rosy, as you’re about to find out. Every combustion process produces byproducts. In our beloved diesel engines, the main byproduct is soot, which is mostly carbon-based.
Every engine has a crankcase ventilation system, or PCV, which allows oil vapors to enter the intake. On its own, this is normal and harmless. But when soot from the EGR is added—remember, it routes sooty exhaust back to the intake—things get problematic. Soot and oil combine to form a sludge.
Initially, it’s not a big problem. There’s no noticeable impact on power, fuel consumption, or overall reliability. But as the buildup increases, it eventually clogs the engine’s airways, and this is where the problems snowball.
When an engine’s breathing capacity is reduced, it naturally produces more soot, which ends up in the intake, potentially to the point where the car becomes undriveable. And if that’s not bad enough, it gets worse—much worse.
As soot production increases, the Diesel Particulate Filter (DPF) is put under greater stress, eventually leading to failure. This is often the first time your engine visits a mechanic. You’d be surprised how frequently they attempt to clean the filter or eventually replace it—a very costly procedure. Depending on the make and model, it’s not unusual for costs to reach up to 5,000 euros, with most around 2,500 euros. But the problem isn’t really fixed; only the consequences are addressed, at best.
That car with a new DPF will likely be back in the garage within a year. The new filter can handle the overload for a while, but it’s not a permanent solution.
This brings us back to the cooperation—or lack thereof—between automakers and governments. Every new car in the showroom meets its emission targets, especially in the post-VW scandal era. But the good news stops there. As a car accumulates thousands or tens of thousands of kilometers, buildup begins, and real emissions start to increase.
Yes, you might pass an annual inspection, but the emissions measured at your ITV station are quite different from what truly matters.
Back to My Point
Yes, manufacturers can build systems that comply with regulations, but nobody seems to care about what happens when a car is seven years old. Manufacturers don’t provide any information on maintaining the engine’s condition. I’ve personally worked in several dealerships, and there are NO instructions on cleaning or maintaining the engine properly, nor for the fuel delivery components.
A smoky diesel usually has three possible causes—or a combination of them: lack of air, malfunctioning injectors, or serious mechanical wear and tear. This is where I see the conflict. Manufacturers install emission-control systems in the most inconvenient locations, making it nearly impossible to clean the engine’s airways without special tools and considerable mechanical expertise.
In conclusion, the system—hated by many car owners—could work much better if it were designed with maintenance in mind. The simplest solution would be a filter that could be replaced or, better yet, cleaned at every oil change. Sadly, this is not the reality we face.
To wrap up, take a look at these pictures. This is a 2017 BMW 2.0d with 179,000 km. The car came in with low power and DPF problems. Believe it or not, this is the intake manifold—responsible for allowing air into the engine—before and after cleaning. Of course, the cleaning doesn’t stop there. The air channels also need attention, and sometimes they are even harder to clean.
But now, this is a happy, powerful engine with many more enjoyable kilometers ahead.
