What Causes Carbon Build Up?

"Understanding Carbon Build-Up in Modern Engines"

Modern engines, despite their advanced technology, face a persistent issue: carbon build-up. But what exactly is carbon build-up? What causes it? How do you avoid it and what can you do to clean off the carbon deposits.

The biggest cause of performance and economy drops is generally down to carbon build up, and it's happening all the time.

Some engines are worse than others and it seems that older engines which used port injection pretty much avoided this problem, so let's look at the reasons why and learn what we can do about this to avoid carbon build up in the first place.

The Nature of Carbon Build-Up

Years ago we talked about a decoke, where the carbon deposits inside the engine/exhaust/headers and manifold were removed.

This was not a significant problem and I still remember people telling me that the carbon helped improve performance by reducing the clearance inside the cylinders - I'll let you discuss that one in the comments - is that a fact a myth or a bit of both?

The issue however is when this builds up on the intake valves and head, it will restrict airflow and this will be the cause of a drop in performance and economy.

Carbon build-up refers to the accumulation of carbon deposits on various engine parts, such as intake valves, combustion chambers, and fuel injectors.

These deposits form because of incomplete combustion of fuel. When fuel doesn't burn entirely, it leaves behind carbon residue.

Lets discuss the common causes of carbon build up and then look at some solutions, preventions or advancements from manufacturers that improves the issue.

Causes of Carbon Build-Up

Direct Injection Engines- Modern engines often use direct injection (DI) technology. DI engines inject fuel directly into the combustion chamber, improving efficiency and power. However, this method also means that fuel doesn't pass over the intake valves to clean them, leading to carbon deposits. These carbon deposits can also build up around the intake manifold restricting flow and lowering performance.

PCV-The engine pressure internally is regulated, ideally a slight negative pressure is desirable as this prevents leaks of both fluids and vapours. The vapour inside the engine comprises carbon particles, oil particles, moisure and other combustion by products. Primary cause of carbon build up is this sticky wet mixture depositing on the valves and causing the carbon from the EGR to stick and solidify.

EGR - Exhaust gases are partially vented back into the intake to aid fuel economy and improve emissions. Any carbon or soot in the exhaust will flow into the intake and potentially clog up anything from the EGR to the Combustion chamber.

Low-Quality Fuel- Using low-quality or contaminated fuel can contribute to carbon build-up. These fuels may contain impurities that don't combust completely, leaving behind carbon residue.

Short Trips and Cold Starts- Frequent short trips and cold starts prevent the engine from reaching optimal operating temperature. In these conditions, fuel doesn't burn completely, increasing the risk of carbon deposits.

Consequences of Carbon Build-Up

Reduced Performance: Carbon deposits can restrict airflow in the intake valves, reducing engine performance. You might notice decreased acceleration and overall power.

Lower Fuel Efficiency: Blocked or partially blocked intake valves make the engine work harder, using more fuel to achieve the same power output, thus lowering fuel efficiency.

Increased Emissions: Carbon build-up leads to incomplete combustion, producing more harmful emissions like carbon monoxide and hydrocarbons.

Engine Knocking: Heavy carbon deposits can increase the engine's compression ratio, leading to knocking or pinging sounds during operation. This can cause engine damage over time.

Addressing Carbon Build-Up

There are a few things you as a driver can do to improve the situation and there are a few additional preventative mods and processes that will help clean up the carbon.

Regular Maintenance: Routine maintenance, including using fuel system cleaners and periodic engine checks, can help manage carbon build-up.

Bear in mind a fuel system cleaner will never hit the valves or intake, but if the injectors and combustion process is efficient there is less carbon produced by the engine and because it is cleaner burning there is less risk of carbon deposits.

Quality Fuel: Always use high-quality fuel to minimize impurities and incomplete combustion. Choosing the correct grade for your engine is important.

Longer Drives: Occasionally taking your vehicle on longer drives at highway speeds helps the engine reach optimal temperatures, promoting complete combustion and reducing carbon deposits.

Carbon build up seems to accelerate more at low rpm and slow driving, which is why often larger capacity engines that typically reside in lower RPM ranges in everyday use have a bigger problem

Fixes & Prevention.

Mods - an oil catch can will capture the vapours before it hits the intake and will in most cases dramatically improve the rate at which carbon build up happens. Without this sticky coating the carbon will generally flow into the engine more easily.

EGR delete - the EGR is often blamed for carbon build up, but one should first ask why is there so much carbon in the exhaust, an efficient engine will burn cleanly. EGR deletes will not be legal in many areas a regions as this affects emissions.

Port Injection - Spraying fuel (gasoline/petrol) onto the intakes will really help clean off the carbon deposits, fuel is a great cleaner thanks to the additives they contain but primarily because it is a solvent.

Manufactures have started adding port injection which is active at certain times, particularly the start up/warm up cycle.

You can also get port injection kits, which were primarily used for people wanted to use alternative fuels like Ethanol and water/methanol mixes

Cleaning Carbon

Intake sprays - asking a spray to make a difference in 10-20mins is pretty unreasonable, they are also quite fiddle to use and you risk hydrolock if you spray too much into the intake at lower RPMS.

In fairness they will do SOME cleaning and really need to be used regularly. I had a professional intake clean done on my TDi using BG products - this proved very effective but required a long application and precise delivery of the cleaner in the intake.

It cost me around £70 and I saw better fuel economy and increased power afterwards. (mileage was at 80,000 for anyone curious.)

Walnut blasts small pieces of walnut shell are blown at the intake. Walnut is hard enough to break through the carbon but it burns easily and will not harm the metal components in the engine.

Physical removal of intake and cleaning this often involves some type of abrasive and or a solvent. Care should always be taken to avoid dumping/dropping stuff into the cylinders so rotation of the engine and ensuring the valves are closed, and cleaning with an air line before moving on to the next cylinder.

I have heard of sandblasting, which should only be done when the head is removed the sand particles can get into the engine and cause all sorts of problems because sand doesn't burn, it melts.

Understanding and addressing carbon build-up can keep modern engines running smoothly. Regular maintenance and mindful driving habits play crucial roles in mitigating this common issue. Check out my other videos on EGR & PCV as I have only briefly mentioned them in this video.

This article is flagged for an update, so please pass on specific tips below that I can include. All articles, and content was written by me, Waynne Smith TorqueCars founder. Some outlines are just too general so I appreciate your feedback and suggestions. This entry was filed under Articles, Car care. You can leave a response below or join our forum to discuss this article and car modification in detail with our members.

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