If someone asks you which is better, mineral oil or synthetic oil? I believe everyone will choose synthetic oil. But why is synthetic oil better? Some people think it is because synthetic oil can maintain a longer maintenance cycle; others think that synthetic oil is expensive, and the more expensive it is, the better it is. In fact, these views are too one-sided. Today we will talk about how synthetic oil is better than mineral oil!
Differentiation between mineral oil and synthetic oil
To distinguish between types of oil, we have to start with the composition of air compressor oil. Air compressor oil is actually composed of base oil and additives. Let's put additives aside and talk about base oil first. The American Petroleum Institute (API) classifies base oils according to sulfur content, saturated hydrocarbon content, and viscosity index. The higher the sulfur content, the easier it is for the oil to deteriorate; the lower the saturated hydrocarbon content, the worse the lubrication performance of the oil, and it is also easy to produce sludge; and the lower the viscosity index, the greater the impact of temperature on the oil performance.
According to the above standards, API divides base oils into 5 categories:
Class I base oil, sulfur content greater than 0.03%, saturated hydrocarbon content less than 90%, and viscosity index between 80-120. This type of base oil is prone to sludge, and has poor stability and consistency.
Class II base oil, sulfur content less than 0.03%, saturated hydrocarbon content greater than 90%, and viscosity index between 80-120. The antioxidant capacity of this type of base oil is improved compared to Class I base oil.
Class III base oil, sulfur content less than 0.03%, saturated hydrocarbon content greater than 90%, and viscosity index greater than 120. This type of base oil has good stability and consistency, but the cost is slightly more expensive than the first two types of base oil.
Class IV base oil, the full name is Poly Alpha Olefin (polyalphaolefin), which is commonly known as PAO. This type of base oil has excellent stability and consistency, and of course the price is also higher.
Class V base oil, other base oils except the first four, mainly include polyalkylene glycol (PAG), silicone oil, ester oil, etc. This type of base oil can further improve the performance of the engine oil and is the most expensive.
After understanding the base oil, we can start to distinguish between mineral oil and synthetic oil. Mineral oil usually uses Class I and Class II base oils, while synthetic oil usually uses Class IV and Class V base oils. Therefore, synthetic oil not only has obvious advantages over mineral oil in terms of performance, but also has a slightly higher price. Here we should especially talk about Class III base oil. It is made of crude oil like Class I and Class II base oils. In theory, it should also be considered as mineral oil. However, because its performance in all aspects is close to synthetic engine oil, and it has been hydroisomerized, some merchants also promote engine oil using Class III base oil as synthetic oil.
Compared with mineral engine oil, the main advantages of synthetic engine oil are reflected in four aspects, the first of which is shear resistance. Since the base oil viscosity index of mineral oil is low, more additives are needed to increase the viscosity index (additives are mentioned here again, don't worry, I will talk about it in detail later), so as to reduce the impact of temperature on oil performance.
However, under high temperature conditions, the viscosity index additive molecules will be sheared and lose their original efficacy, and the viscosity index of mineral oil will also decrease. This means that when the engine is running at high load, the mineral oil film will tear, reducing the lubrication and protection of the engine.
The base oil of synthetic oil itself has a relatively high viscosity index, so the content of viscosity index additives is less than that of mineral oil, and the performance attenuation under high load conditions is also lower, which greatly reduces the engine wear caused by oil film tearing.
The second point is the cold start performance of air compressor oil. As we all know, the fluidity of air compressor oil will decay as the temperature decreases. Especially in cold areas, if the low-temperature fluidity of air compressor oil is very poor, then when the air compressor is cold started, the wear will be aggravated because the air compressor oil cannot play a lubricating role in the first time.
Since the performance of synthetic oil is less affected by low temperature than mineral oil, synthetic oil protects the main engine better than mineral oil of the same grade when cold starting in low temperature environment. For example, the viscosity of 5W30 Castrol Silver Guard (mineral oil) at minus 30° is 5830mPa.s, while the viscosity of 5W30 Castrol Super Guard (synthetic oil) at minus 30° is 5700mPa.s. The two oils have the same grade, but the fluidity of synthetic oil at minus 30° is significantly better than that of mineral oil, and the cold start performance is also stronger.
The third point is the consistency of air compressor oil. The size of mineral oil molecules is very random. Small oil molecules are very easy to evaporate and consume, while large oil molecules are relatively stable. When the small oil molecules evaporate, the remaining large molecules will reduce the fluidity of the oil, causing the engine to wear more due to insufficient lubrication of the oil. On the other hand, the oil molecules of synthetic oil are highly consistent and evenly arranged together, so the fluidity of synthetic oil will not be greatly reduced due to volatilization and consumption, and it can provide longer protection for the engine.
The fourth point is the antioxidant property of air compressor oil. After we add air compressor oil to the air compressor, as the air compressor runs and stops every day, the air compressor oil also begins an infinite cycle of life from heating to cooling. In this process, the air compressor oil slowly begins to oxidize and deteriorate when in contact with the air, and the fluidity gradually becomes worse and worse, resulting in a decrease in the protective effect on the air compressor head.
Compared with mineral oil, synthetic oil has an outstanding advantage in antioxidant property, so when the life cycle of most mineral oils is only a few thousand kilometers, synthetic oil can provide good protection and lubrication for the engine even in a service life of tens of thousands of kilometers.
About additives
Let's remember a conclusion first: a good base oil is the basis of a bottle of high-quality oil. If the base oil is not good, no matter how good the additive formula is, it will be useless. However, additives can often make up for some deficiencies of mineral oil and further enhance certain characteristics of synthetic oil. Let's briefly talk about the types and uses of additives.
Viscosity index improver: The lower the viscosity index, the greater the impact of temperature on the performance of the engine oil. What if the viscosity index is not enough? It doesn't matter, add additives to make up for it!
Antioxidant: After the engine oil is oxidized, not only will the lubrication and protection function decrease, but the organic acid produced by the oxidation reaction will also corrode various engine parts. Therefore, it is very important to improve the antioxidant property of the engine oil.
Alkaline additives: Since the organic acid produced by the oxidation reaction will corrode the engine, and the sulfur element contained in the fuel will also produce acidic sulfides after combustion, alkaline additives are needed in the engine oil to achieve the purpose of acid-base neutralization.
Anti-wear agent: In the case of lack of engine oil lubrication in the main engine such as air compressor oil film rupture and air compressor cold start, the anti-wear agent attached to the metal surface can minimize the wear of the main engine.
Dispersant: Engine oil sludge is one of the factors that harm the main engine of the air compressor. Dispersant can effectively prevent the accumulation and precipitation of sludge and avoid blockage of the engine oil circuit.
Cleaner: Carbon deposition is one of the most troublesome problems of air compressor main engine. With the help of cleaner, carbon deposition can be significantly suppressed.
Defoamer: The air compressor oil is repeatedly stirred in the engine, which will naturally produce a lot of foam. These foams have two harmful effects: first, the foam reduces the protection of the oil to the engine; second, the foam increases the surface area of the air compressor oil in contact with the air, accelerating the oxidation of the oil. In order to reduce the harm caused by the above two situations, defoamers are also indispensable.
The above are the more common types and functions of additives in engine oil. Different air compressor oil brands will adjust different additive formulas according to the characteristics of their own product base oil, but the basic principle is the same.