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.
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).
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.
4. VI improvers
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.
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.
- 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.