Engineering Explained recently broken down several reasons that synthetic oil is superior to conventional motor oil. You can check out the reasons below, but we’ll also go over a couple of reasons why synthetic oil is worth it.

Conventional Oil

Conventional motor oil is composed of a refined form of crude oil, created by exposing it to specific amounts of heat and chemical solvents to remove impurities. This oil often receives several additives to keep it stable at higher temperatures and occasionally agents to make it move through the engine more reliable, as well as detergents to de-gunk the engine components. 

Conventional oils suffer from some minor drawbacks, such as particle size inconsistency and high-temperature breakdown. The high-temp breakdown can be combated to a degree by employing carbon-based polymers which expand as the oil warms up, increasing viscosity. 

Synthetic Oil

Generally speaking, synthetic oil starts with a blend of several base oils, such as mineral oil, refined petroleum, and so on. Once these have been created with consistent particle sizes, additives are added to the synthetic oil for the following purposes:

• Anti-foaming agents – These prevent the oil from foaming as it churns through the engine. 
• Rust fighters – Rust fighters help keep engine components from breaking down over time—rust affects the surface of the metal and can result in pitting, making the metal more susceptible to breaking.
• Dispersants – For making the oil spray more consistently and better.
• Antioxidants – Similar to rust fighters, antioxidants prevent engine components from oxidizing. This may include seals, aluminum and cast iron pieces, and even parts, like the crankshaft, which are mostly submerged in oil.
• Anti-wear agents – Anti-wear agents are used to prevent metal-on-metal contact during vehicle operation. Extreme pressure (EP) agents are commonly used in gear oil for transmissions and similar applications. 
• Viscosity Index Improvers (VIIs) – VIIs are generally carbon-based polymers, bunches of carbon atoms bound together. VIIs shrink when they are cold, making oil thinner, and expand when hot, making the oil thicker. VIIs have given us variable viscosity oil (e.g. 5W30). The W stands for Winter, indicating oil viscosity at low temperatures.

The main drawback of synthetic oil? It is expensive, commonly around double the cost of conventional oils. Readers should know that synthetic oil can sometimes cause leaks in engines. This is commonly caused by detergents removing gunk-plugs from small holes in the seals. 

Older synthetic oil products used alcohol-derived esters, but sometimes alcohol made it into the final product, resulting in increased seal wear. Newer synthetic oils have much stricter purity and quality assurance requirements, meaning this is much less likely to be an issue, however, some pre-1990 automobiles are recommended for use only with conventional oil.

Semi-Synthetic Oil

Semi-synthetic oil combines several benefits of synthetic oils with a lower cost, more like that of conventional oil. They include synthetic compounds, like VIIs, rust fighters, and anti-wear agents, but often have the same, irregular particle size that conventional oil does. This lack of consistency and oil base quality are two reasons it costs so much less than synthetic motor oil, yet has many of the same benefits. 

What makes synthetic oil so much better for your engine? Consistency and composition. Synthetic oil contains chemicals and compounds that improve where traditional motor oils failed. By reducing wear, preventing oxidation and foaming, and altering the viscosity of the oil based on temperature, synthetic oil provides excellent protection for your vehicle.

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