Motor oil types: Which one to choose? Comparison between semisynthetic, synthetic and mineral oil

Introduction

The proper functioning and longevity of a vehicle’s engine depends to a large extent on the type of lubricant used. Engine oils not only reduce friction between internal parts, but also help dissipate heat and keep the engine clean. However, not all oils are the same, and choosing the right one can make a difference in vehicle performance. In this article, we will analyze the motor oil types, comparing the characteristics, advantages, and disadvantages of mineral, semi-synthetic and synthetic oil.

Importance of motor oil

Engine oil plays a fundamental role in vehicle performance. Among its main benefits are:

• Lubrication of moving parts to reduce wear.
• Cooling of the engine by dissipating the heat generated by friction.
• Cleaning of impurities and sediments accumulated in the engine.
• Prevention of rust and corrosion of internal components.

However, each type of oil has specific characteristics that make it more or less suitable depending on the type of engine and the conditions of use.

Motor oil types according to viscosity

The Society of Automotive Engineers (SAE) classifies engine oils, according to their viscosity, into two main types that determine their behavior at different temperatures:

Monograde oils.

These are oils that maintain a stable viscosity at a single temperature, without viscosity index improver additives, and are identified by having a single SAE number.

• Examples: SAE 30, SAE 40, SAE 50.
• Applications: Older engines and industrial machinery.
• Limitations: Not suitable for variable climates, as they become too thick when cold and too fluid when hot.

Multigrade oils

Designed to adapt to different temperatures, improving performance in cold starts and high temperatures.

• Examples: SAE 5W30, SAE 10W40, SAE 15W-40. SAE 20W-50.
• Code interpretation: The number before the “W” (Winter) indicates the cold viscosity. The lower it is, the more fluid the oil will be at low temperatures. The number after the “W” indicates the hot viscosity. The higher it is, the greater the thermal stability.
• Advantages: Optimal cold start, engine protection in extreme conditions and suitable for different climates and driving styles.

Types of motor oil according to their production

This refers to the different processes used to produce motor oils. They are classified according to their processing and chemical composition into three main types: mineral, synthetic and semi-synthetic. Each has specific characteristics that affect engine performance and durability.

Mineral oil

It is obtained directly from petroleum through refining processes. It is the most basic and economical type of lubricant, suitable mainly for older engines without high performance requirements.

• Advantages: Affordable price and good lubrication in engines of classic design.
• Recommended use: Older vehicles or with low-demanding engines and for environments with moderate temperatures.
• Disadvantages: Lower resistance to extreme temperatures, they degrade faster than synthetic oils, therefore, they require more frequent changes and are more prone to generate residues and sediments.
• Frequency of change: It is recommended every 5,000 km at the most.

Semi-synthetic oils

These are a blend of mineral and synthetic oils offering a balance between cost and performance. The proportion of the mixture varies according to the manufacturer, but is in the range of 70% – 80% mineral oil and 20% – 30% synthetic oil.

• Advantages: Higher thermal resistance than mineral oils, but lower than synthetic oils, better cost-benefit ratio and good protection against engine wear. Less generation of sediments and residues and longer durability than mineral oil.
• Recommended use: Daily use vehicles with modern engines. Drivers looking for better protection of their vehicles without spending too much.
• Disadvantages: They do not have the same durability as synthetic oils.
• Frequency of change: The frequency varies according to each manufacturer, but on average it is recommended to change it every 10,000 Km. The manufacturer’s recommendations should always be considered.

Synthetic oils

They are chemically produced with lubricant bases designed to offer superior performance.

• Advantages: Increased thermal stability and resistance to oxidation, improved performance in extreme temperatures (high and low) and reduced formation of deposits and residues in the engine, longer service life and reduced frequency of changes, reduced engine wear in extreme conditions.
• Recommended use: High performance and latest generation engines, vehicles subjected to extreme conditions (cold or hot climates, sporty driving, heavy loads).
• Disadvantages: More expensive, not always compatible with older engines.
• Frequency of change: The frequency varies according to each manufacturer, but on average it is recommended to change it every 20,000 Km. The manufacturer’s recommendations should always be considered.

Re-refined base oils (RRBO) (Recycled)

It is a lubricant obtained from used oils through advanced processes involving vacuum distillation, dehydration, hydrotreating, among others, to restore their original properties.

Thanks to these technologies, RRBO achieves a quality comparable to that of virgin base oil, meeting the standards of the American Petroleum Institute (API) and the International Lubricants Standardization and Approval Committee (ILSAC) at a lower cost, making it an attractive option.

With the growing regulatory and technological acceptance, RRBO is positioned as a sustainable and efficient alternative, capable of replacing traditional oils without affecting the functionality of engines and equipment. RRBO has been brought to a level of quality necessary for use in most passenger car and heavy-duty vehicle engines.

API classification of engine lubricating oils

API classifies oils into two main series: “S” Series for gasoline engines and “C” Series for diesel engines. Each category has its own specifications and progressive improvements to suit the needs of modern engines.

S” Series (Service) – Gasoline Engines

This series is intended for vehicles with gasoline engines and is represented by the letter “S” followed by another letter indicating the evolution of the standard.

Characteristics of each specification of the “S” Series

Classification	Introduction year	Main features
API SA	1930	Oil without additives, already obsolete. Not recommended for modern engines.
API SB	1951	Contains basic additives to reduce oxidation and deposit formation.
API SC	1964	Better protection against wear and oxidation, suitable for engines from the 60’s.
API SD	1968	Increased protection against deposits and wear.
API SE	1972	Improved resistance to oxidation and corrosion.
API SF	1980	Increased protection against wear and sludge formation.
API SG	1989	Includes more advanced detergent and dispersant additives.
API SH	1993	Introduces stricter quality control standards.
API SJ	1996	Increased resistance to deposit formation at high temperatures.
API SL	2001	Reduced oil consumption and improved thermal stability.
API SM	2004	Improved protection against oxidation and deposits, reduced friction.
API SN	2010	Increased protection for high performance engines and compatibility with ethanol fuels.
API SN Plus	2018	Low speed pre-ignition protection (LSPI) on turbocharged engines.
API SP	2020	Latest specification, optimized for modern engines with turbochargers and lower fuel consumption.

Note: Each new specification is backward compatible, which means that an API SP oil can replace an API SN or earlier oil.

C” Series (Commercial) – Diesel Engines

This series is specifically for diesel engines, used in cargo vehicles, heavy machinery and industrial equipment. It is identified by the letter “C” followed by another letter and number.

Characteristics of each “C” Series specification

Classification	Introduction year	Main features
API CA	1940	Basic protection against corrosion and deposits in older diesel engines.
API CB	1949	Increased resistance to oxidation and deposits.
API CC	1961	Improved protection against deposits and wear in heavy duty engines.
API CD	1955	First standard with soot and deposit control in high power engines.
API CE	1983	Additives for high torque diesel engines.
API CF	1990	Designed for indirect diesel engines and modern injection systems.
API CF-4	1990	Wear protection for four-stroke engines under high loads.
API CG-4	1995	Reduced emissions and greater thermal stability.
API CH-4	1998	Complies with stricter emission regulations.
API CI-4	2002	Designed for engines with exhaust gas recirculation (EGR).
API CJ-4	2006	Reduction in sulfated ash content and compatibility with diesel particulate filters (DPF).
API CK-4	2016	Protection against oxidation and wear in low emission engines.
API FA-4	2016	Similar to API CK-4, but with lower viscosity to improve fuel efficiency.

Manufacturing process of mineral and synthetic oils

These oils have fundamental differences in their manufacturing process, which influences their performance, durability, and applications.

Mineral oil manufacturing process

They are obtained directly from crude oil through a refining process. The process includes:

• Fractional distillation: The different compounds are separated from the crude oil at different temperatures.
• Refining: Impurities and unwanted compounds, such as waxes and sulfur, are removed.
• Hydrotreating or solventing: Improves thermal stability and resistance to oxidation.
• Blending with additives: Detergents, dispersants, antioxidants and viscosity modifiers are added to improve performance.

Synthetic oil manufacturing process

Produced in laboratories using chemical synthesis processes to create molecules with uniform structure and enhanced properties. Common methods include:

Synthetic Vs. mineral oil

When comparing base oils of similar viscosity, fully synthetic base oils demonstrate better performance than conventional base oil in the following ways:

• Synthetic oils burn less (have lower volatility) than conventional oils in high temperature situations, such as in an automotive engine.
• Synthetic oils move better at lower temperatures and continue to move at extremely low temperatures that conventional oils would not move.
• Synthetic oils contain fewer impurities such as sulfur and wax.
• Synthetic oils adhere better to surfaces.

Comparative table of oils

Features	Mineral oil	Semi-synthetic oil	Synthetic oil
Viscosity	Low stability	Medium stability	High stability
Durability	Low	Medium	High
High temperature performance	Low	Medium	High
Pricing	Economic	Intermediate	High
Waste generation	High	Medium	Low
Recommended for	Old engines	Daily use	High performance

Is it safe to change from mineral to synthetic oil in a high mileage engine?

It is considered safe, but some precautions should be taken. Synthetic oils offer better protection, thermal stability and internal cleanliness, which can benefit worn engines. However, in engines with aged seals or accumulation of deposits, synthetic oil, having greater detergent capacity, could remove residues and cause small leaks.

Recommendations for engine oil change

• Check compatibility: Consult the vehicle’s manual to ensure that the synthetic oil meets the manufacturer’s specifications.
• Use an oil with the proper viscosity to avoid drastic changes in lubrication.
• Preferably make a gradual change, suggesting the use of a semi-synthetic oil before switching to a 100% synthetic oil.
• Inspect the condition of the engine: If there are previous leaks or high oil consumption, it may be better to keep the mineral.
• Ensure cleanliness of the strainer filter and engine sign.

Factors to consider when choosing a motor oil

In order to choose the right oil, it is essential to consider the following aspects:

• Climatic conditions: Low viscosity oils work best in cold weather, while higher viscosity oils offer better protection in high temperatures.
• Age: If the engine is old, a mineral oil may be sufficient and for modern or high performance engines, it is better to opt for semi-synthetic or synthetic.
• Type of engine and manufacturer’s specifications: Always follow the recommendation of the vehicle’s manual regarding viscosity and type of oil.
• Conditions of use: In cold or hot climates, an oil with high thermal stability is recommended. A high-performance or heavily loaded engine requires oils with higher thermal and oxidation resistance.
• Oil change frequency: If you are looking for longer oil change periods, synthetic oil is the best option.
• Cost-benefit: Although synthetic oil is more expensive, it can save costs in the long run by reducing engine wear and oil change frequency.

Conclusions

Selecting the right engine oil is crucial to ensure engine efficiency and durability. Mineral oil is an economical choice for older engines, while semi-synthetic oil offers a balance between performance and cost. On the other hand, synthetic oil provides maximum protection and durability, making it ideal for modern, high-performance engines.

The choice of lubricant will depend on the specific needs of the vehicle and the user’s budget. By following the manufacturer’s recommendations and considering the operating conditions, engine performance can be optimized and engine life extended.

References

1. https://india.gulfoilltd.com/blog/engine-oil-grades-types-classifications
2. https://www.infineuminsight.com/en-gb/resources/api-certification-marks-and-symbols/