How Sulfur Content Impacts Lubricant Performance & Equipment Protection

Have you ever wondered how modern engines stay clean while still working so powerfully? With the arrival of Diesel Particulate Filters (DPFs) and Gasoline Particulate Filters (GPFs), a new type of engine oil became very important—low-SAPS oil.

Older engine oils used strong additives like phosphorus and sulfur because they help protect the engine from wear and oxidation. But the problem is that these same additives can slowly damage the vehicle’s emission control systems, which are designed to reduce pollution. To fix this issue, oil manufacturers created special engine oils with much lower levels of sulfur and phosphorus. These are called low-SAPS or low-emission oils.

As the name suggests, low-SAPS oils contain fewer sulfated ash, phosphorus, and sulfur particles. This helps the exhaust system work better, keeps the engine cleaner, and also reduces harmful emissions. At Fubex Lubricants, we offer high-quality lubricants for all types of engines. Enjoy fast shipping, a price match guarantee, and no-questions-asked returns. Need help choosing the right oil? Call us at +971 50 544 9614 — our friendly team is ready to assist!

Awais I., Sales Director, says, “Understanding how sulfur content impacts lubricant performance is not just about controlling additives—it’s about protecting valuable equipment, preventing unexpected wear, and ensuring smooth, efficient, and long-lasting machine performance in every operation.” 

If you’re still curious about how these oils work and why they matter so much, this guide will help you understand everything in a simple way.

What is SAPS Content?

Every engine oil, whether it is mineral oil or synthetic oil, is made with a base oil and special additives that improve performance.

These additives help the oil protect the engine better. Some common additives include antioxidants, corrosion inhibitors, viscosity index improvers, anti-wear agents, and extreme pressure additives. These ingredients help the oil last longer, reduce wear, and keep the engine running smoothly.

Two commonly used additives are phosphorus and sulfur. They are helpful because they protect engine parts from damage and oxidation. However, using these additives can also create SAPS content in engine oil. Too much SAPS can sometimes cause engine problems, lower fuel efficiency, and increase harmful gas emissions. SAPS stands for sulfated ash, phosphorus, and sulfur. Here is what you should know about each one:

Sulfated Ash

Sulfated ash is a test that measures the amount of metallic material left behind when engine oil burns inside the engine. This material mainly comes from detergent and anti-wear additives used in engine oil.

When additives that contain phosphorus and sulfur burn, they leave ash particles in the oil. These metallic particles cannot burn away or disappear. Over time, they build up inside the Diesel Particulate Filter (DPF) and reduce its life. They can also damage catalytic converters by stopping them from removing harmful gases from the exhaust.

Phosphorus

Phosphorus is an important additive that helps reduce friction and wear between moving engine parts. It is commonly found in additives called Zinc Dialkyldithiophosphate (ZDDP). This additive forms a protective layer on metal parts and helps protect the engine from damage caused by friction.

Phosphorus is also found in corrosion inhibitors, friction modifiers, antioxidants, and extreme pressure additives. However, when phosphorus burns, it can block the DPF and harm the Gasoline Particulate Filter (GPF) in petrol vehicles.

Sulfur

Sulfur is another additive used in engine oil. It helps prevent oxidation and also protects engine parts from wear. When sulfur burns, it creates sulfur oxides and ash particles. These particles can build up and block the DPF, especially when the oil becomes thick.

Sulfur mainly comes from corrosion inhibitors, friction modifiers, antioxidants, and anti-wear additives like ZDDP.

What is Low-SAPS Oil?

Phosphorus and sulfur additives help protect the engine from wear, friction, and oxidation. However, using too much of these additives can damage the catalytic converter and other exhaust system parts. In some cases, the metallic particles can also harm the engine.

Because of this, the European Automobile Manufacturers’ Association (ACEA) has set limits on how much phosphorus and sulfur can be used in engine oil. To solve this problem, lubricant manufacturers started developing new additives that produce less ash while still protecting the engine well.

This led to the creation of low-SAPS oils. Low-SAPS engine oil contains low levels of sulfated ash, phosphorus, and sulfur. These oils are also called low-ash engine oils because they create less ash during combustion. Low-SAPS oils use advanced low-emission additives and are specially made for vehicles with Diesel Particulate Filters (DPFs) and Three-Way Catalytic Converters (TWCs).

Because they produce less ash and contain lower amounts of sulfur and phosphorus, low-SAPS oils help extend engine life. They also improve the performance of the exhaust gas cleaning system and help reduce harmful emissions.

ACEA Oil Rating

ACEA is a European system used to classify engine oils. It is similar to the API classification system used in the United States.

One major difference is that ACEA standards are usually stricter than API standards.

ACEA divides engine oils into different categories:

• A: Oils made for petrol engines
• B: Oils made for light-duty diesel engines
• C: Oils made for vehicles with Three-Way Catalytic Converters (TWC) and Diesel Particulate Filters (DPF)
• E: Oils made for heavy-duty diesel engines

Low-SAPS and mid-SAPS oils belong to the C category because they are designed to work safely with catalytic converters and DPF systems.

ACEA also uses numbers to divide C-category oils into different grades. These include C1, C2, C3, C4, and C5 engine oils.

Low-SAPS vs. Mid-SAPS Lubricants

Engine oils are grouped based on how much SAPS they contain. SAPS means sulfated ash, phosphorus, and sulfur.

• C1 and C4 oils are called low-SAPS oils
• C2, C3, and C5 oils are called mid-SAPS oils

Mid-SAPS oils contain less ash than normal engine oils. Because of this, they are safer for modern engine systems like catalytic converters and DPFs. Low-SAPS oils contain even less ash than mid-SAPS oils. They are specially made for very sensitive engine parts and advanced after-treatment systems.

In simple words, low-SAPS oils are cleaner, while mid-SAPS oils are still cleaner than regular oils but not as strict as low-SAPS oils.

Properties of Low-SAPS C-Grade Oils

Each C-grade engine oil is made a little differently. That means they don’t all work the same way. They have different chemical mixes and performance levels.

Some oils in this group, like C2, C3, and C5, may look similar, but they behave differently in heat and pressure conditions. This is called HT/HS (High Temperature / High Shear).

• Lower HT/HS = better fuel saving
• But it may not work in every engine

Now let’s look at each type in a simple way.

ACEA C1 Engine Oils

C1 oils are very light and stable oils. They are used in cars that have Diesel Particulate Filters (DPF) and Three-Way Catalysts (TWC).

They are also used in engines that need:

• Low friction
• Low SAPS content (very low ash)
• Strong protection with less wear

These oils have very low ash levels (less than 0.5%) and a minimum HT/HS level of 2.9 cP. They are mostly available in 5W-30 viscosity.

In simple words, C1 oils are very clean oils that protect the engine and also protect the emission system.

ACEA C2 Engine Oils

C2 oils are also stable and work well in modern engines with DPF and TWC systems. They are used in engines that need a balance between protection and fuel saving. These oils have:

• Mid-SAPS content (less ash than normal oils, but more than C1)
• Ash level less than 0.8%
• Minimum HT/HS of 2.9 cP

C2 oils can come in different viscosities like 0W-30 or 5W-30. In simple words, C2 oils give a good balance between engine protection and fuel efficiency.

ACEA C3 Engine Oils

C3 oils are strong and stable oils used in many modern petrol and diesel engines. They are also safe for vehicles with DPF and TWC systems.

These engines need:

• Mid-SAPS content (ash below 0.8%)
• Higher protection under heat and pressure
• Minimum HT/HS of 3.5 cP

C3 oils come in different viscosities like 0W-30, 5W-30, and 5W-40. In simple words, C3 oils are stronger oils made for engines that need extra protection under tough driving conditions.

Can We Use Different C-Grade Oils Interchangeably?

No, ACEA C-grade engine oils cannot be freely swapped or used in place of each other. For example, you should not use C1 oil in an engine that needs C3 oil, because C1 has a much lower level of sulfated ash and different performance requirements. Using the wrong type of oil can cause engine problems. It may reduce engine performance, affect fuel efficiency, and even shorten the engine’s life.

That’s why most car manufacturers give clear instructions about which oil should be used. Always check the OEM (vehicle manufacturer) guide before choosing any C-grade engine oil.

HT/HS Viscosity Ranges for Low-SAPS Lubricants

HT/HS stands for High Temperature / High Shear. It shows how thick or thin engine oil is when the engine is very hot (around 150°C). It also tells us how well the oil can protect fast-moving engine parts like piston rings, valve parts, and gear contact areas.

In simple words, HT/HS helps us understand:

• How well the oil protects the engine in tough conditions
• How much fuel the engine can save

If HT/HS is higher, the oil is thicker and gives better protection against wear. If HT/HS is lower, the oil is thinner and helps improve fuel economy, but protection is a bit lower.

HT/HS is measured in a unit called millipascal second (mPa·s).

• Above 3.6 mPa·s = normal thickness
• Below 3.6 mPa·s = lower viscosity (thinner oil)

HT/HS is also very important in ACEA oil standards. Some ACEA oil types like A2, A3, B2, B3, and E series need HT/HS above 3.6 mPa·s, which means they are thicker oils.

Low-SAPS and mid-SAPS oils are made for special engines, so their HT/HS levels can be different:

• C1 and C2 Oils: above 2.9 mPa·s
• C3 and C4 Oils: around 3.5–3.6 mPa·s
• C5 Oils: at least 2.6 mPa·s (thinner for better fuel saving)

Because every engine is different, it is very important to always use the oil grade recommended by your vehicle manufacturer.

Final Takeaways

Even though engine oil makers try to reduce sulfur and phosphorus, these additives are still important because they protect engine parts from wear. But they can also harm the environment and exhaust system over time. That’s why new additives are being developed to replace them while still protecting the engine. 

This is where low-SAPS or C-grade oils are used. These modern oils help protect the engine, extend oil life, and reduce harmful emissions. When choosing the right oil, always check the ACEA grade, viscosity, and HT/HS value to match your engine’s needs.

FAQs

Q1: Is sulfur used as a lubricant?

Yes, sulfur is used in engine oil as an additive to improve protection, reduce wear, and act as an antioxidant. It helps under high pressure and friction, but modern oils use it in controlled amounts to reduce harmful effects.

Q2: Why is sulfur used in gear oil?

Sulfur is used in gear oil because it reacts under high heat and pressure to form a protective layer on metal surfaces. This layer reduces friction and prevents damage like scuffing or galling between gear teeth.