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The basics of lubricants: The quick guide to understanding oil additives (2/9)

Motor oil has become a highly complex product. It uses the exact right combination of additives to make a specific engine type run better and longer. Update yourself on the basics of oil additives in just a few minutes.

Technical Expertise

In our previous article in our series on the basics of lubricants, we introduced you to the concept of base oils. A quick memory refresh:

The foundation of every lubricant is base oil, which comes in two types: Mineral base oils and synthetic base oils. Base oil determines the viscosity – or “thickness” – of a lubricant. When looking at the overall composition of a lubricant, base oils make up 70-90% of a lubricant.

The remaining 10-30% consists of additives, in various combinations. These are chemical components that enhance the oil’s performance. Did you know oil additives are also called dopes? In this second article in the series, we’ll dive deeper into the topic of additives.

Why do we need oil additives?

In theory, you could think base oil would be enough to lubricate an engine. But the reality is different. To name just a few problems that would occur:

  • Oil oxidates. Many materials show a chemical reaction when exposed to oxygen for a certain amount of time. This is called oxidation, and rust (on iron) is a well-known example. Oil can oxidate too, especially at higher temperatures such as inside an engine.
  • Because an engine collects soot, dust, and other particles, the oil would quickly get contaminated and break down or leak out.
  • A base oil’s viscosity fluctuates with temperature. Just like cooking with olive oil, base oil is thicker when it’s cold and runnier when it’s warm. As a result, base oil might have the right thickness in summer but not in winter — or the other way around.

Oil additives solve these challenges and others. They extend a lubricant’s life (and therefore the engine’s), and make it usable throughout the entire year.

Julie Sterkens

At the same time, additives address the fact that engines have become much more complex over the last 10-15 years. Under the pressure to make engines smaller and better performing at the same time, engine manufacturers have introduced many innovative features that demand more sophisticated lubricants. This is where oil additives come in.

The checklist of oil additives

At Wolf, we have been developing new and innovative lubricants since more than 60 years in close collaboration with the major additive suppliers. Oil additives need to possess specific properties to be fit for commercial use. Here are a few important ones.

  • must be fully and fast soluble in base oil
  • generally must be insoluble in water, if not they would be washed out when the oil is exposed to water
  • may not chemically react with other additives or water
  • must be easily manageable and contain an acceptable safety risk

As a side note, for efficiency reasons, oil manufacturers prefer multifunctional additives. These have multiple benefits built-in in a single additive. What are the beneficial characteristics of these additives? We’ll give you the 5 most common additives.

5 additives you should know

Let’s take a look at five common oil additives.

1. Antioxidants
This is probably the most used type of additive. Just like food, for example, oil oxidates, meaning it decomposes under the influence of oxygen from the air at higher temperatures. Antioxidants prevent this. The most commonly used antioxidant is zinc dithiophosphates (or ZDTP).

2. Detergents
A working engine produces several ‘waste products’. Three examples are:

  • deposits formed at high temperature
  • acids that arise from combustion (especially when using sulphurous lubricants)
  • and dust from outside the engine.

Detergent additives ‘clean’ an engine of these and possibly other materials. They contain metal elements such as calcium (Ca), magnesium (Mg) or barium (Ba), which explains why they, in their turn, produce ashes. The amount of ash is expressed by the so-called ash-number that legally cannot exceed certain values.

3. Dispersing additives
There are specific engine deposits that detergent additives cannot handle. Often called sludge is formed at low temperature and during ‘start-stop conditions’. If not dealt with, these deposits would congeal and obstruct oil filters and pipes. Luckily, we have dispersing additives. They keep the deposits and other elements in suspension, so they do not congeal. This is the reason that oil becomes darker when used. Naturally, there is a limit to how many particles an oil can contain. That’s why motor oil gets changed every now and then: The oil has gotten too saturated with sludge and other elements. Follow your car’s manufacturer recommendations for your oil change interval — as you can’t draw any conclusions from the oil color as seen on the dipstick.

4. VI improvers
The viscosity index or VI of a lubricant is an important characteristic. It used to be that engines needed ‘winter oil’ and ‘summer oil’, each with a different VI. Basically, VI improvers turn a lubricant into an all-season oil.
The most important VI improvers are: Polyalkylmetacrylats (PMA), alkene copolymers and polyisobutylenes. They are polymers with high molecular weight, meaning they're viscous or thick (just like honey). That's why they are barely sold in their pure form, but rather as a solution in oil.
One disadvantage of these polymers is that shearing, which occurs in parts of the engine that move at high speed, can decrease their effectivity to control viscosity. We call this shear viscosity loss. Naturally, VI improvers with a low tendency to lose their viscosity are preferred.

As a bonus, VI improving additives can also have dispersing characteristics or can function as pour point depressants.

5. Pour point depressants (PPD’s)

Lubricants must flow evenly, even when it’s cold. But without additives, at lower temperatures oils would show crystallized paraffin particles — think of how olive oil becomes cloudy when it’s cold.
PPD’s avoid that these particles lump together and thus hinder the flowing of the oil. Just as VI improvers, PPDs are polymers.

And that’s just the beginning

There you have them: Five of the most important additives to be aware of.

But there are many more. Anti-wear additives, anti-corrosion additives and friction modifiers are just a few. We'll come to those on another occasion.

In short:
  • The foundation of every lubricant is base oil, while the remaining 10-30% consists of additives.
  • Additives solve oxidation, production of soot particles, and viscosity problems.
  • 5 important additives are: antioxidants, detergents, dispersing additives, VI improvers, and pour point depressants.

Read the first article about base oils.

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