Quick Links
What You Need to Know – Part 2
In Part 1, we discussed what motor oil is made of, including base oils and additives. In this section, we will explore the essential functions that modern motor oil performs inside an engine, followed by an overview of viscosity, SAE viscosity grades, and gasoline engine oil classifications.
Modern motor oils are highly specialized lubricants carefully formulated by engineers and chemists to perform multiple functions simultaneously. The right combination of base oils and additives enables engine oil to protect components, maintain cleanliness, control temperature, and support reliable engine performance.
What Must Motor Oil Do?
Motor oil performs several essential functions inside an engine, including:
Reducing friction and wear
Cleaning and controlling deposits
Transferring heat
Sealing the combustion chamber
Damping mechanical shock
Protecting against corrosion
Transferring hydraulic energy
Each of these functions contributes to engine performance, reliability, durability, and service life.
Minimize Friction
One of the primary functions of engine oil is to reduce friction and wear between moving components.
The lubricant forms a protective film between surfaces, helping minimize direct metal-to-metal contact. This reduces friction and protects components from excessive wear.
Oil’s ability to remain on component surfaces after the engine has been shut down is particularly important during startup. A cold start does not necessarily mean starting the engine in cold weather; it can also refer to starting an engine after it has been stationary for several hours, such as overnight.
Effective lubrication during startup helps reduce wear during one of the most demanding periods of engine operation.
Cleaning Power
Engine oil also helps maintain internal engine cleanliness by carrying contaminants and preventing deposits from accumulating on critical components.
Base oils have varying levels of solvency, which can contribute to the oil’s ability to interact with certain contaminants. However, detergents and dispersants play an especially important role in modern engine oil formulations.
Detergents
Detergents help prevent contaminants and deposits from adhering to engine components, particularly high-temperature components such as pistons and piston rings.
Dispersants
Dispersants help keep contaminants suspended within the oil, reducing their tendency to combine and form sludge or deposits.
Together, detergents and dispersants help maintain engine cleanliness and support reliable lubricant performance.
Cooling
Engine oil also contributes to engine cooling.
Reducing friction helps minimize the amount of heat generated between moving components. In addition, circulating engine oil absorbs heat from areas where direct cooling may be difficult and carries that heat away to locations where it can be dissipated, such as the oil sump.
This makes engine oil an important part of the engine’s overall thermal management system.
Sealing
Engine oil contributes to sealing between components such as the piston rings and cylinder walls.
The oil film helps support the sealing function of the piston-ring system, helping retain combustion pressure within the combustion chamber and reducing the movement of combustion gases into the crankcase.
Effective sealing supports engine efficiency and helps protect the lubricant from excessive contamination by combustion gases.
Dampen Mechanical Shock
Lubricant films can also help cushion mechanical shock between moving components.
A properly formulated oil film can absorb and distribute mechanical energy across contact surfaces, helping reduce localized stress and wear.
By minimizing damaging forces between components, lubrication can contribute to longer component life and more reliable engine operation.
Protect Against Corrosion
Engine oil helps protect internal engine components from rust and corrosion.
Corrosive substances can be produced during combustion or enter the engine through moisture and other contaminants. Engine oil formulations therefore include additives designed to help protect metal surfaces.
Corrosion protection can be achieved by neutralizing certain corrosive materials or by creating a protective barrier between the component surface and corrosive substances.
Transfer Hydraulic Energy
Because engine oil is effectively incompressible under normal operating conditions, it can also serve as a hydraulic energy-transfer medium.
This property is used in systems such as:
Hydraulic valve lifters
Variable valve timing systems
Hydraulic actuators
Other oil-operated engine mechanisms
In these applications, oil pressure is used to operate or adjust engine components.
The Importance of Balanced Additive Technology
Modern engines are becoming smaller, more powerful, more fuel-efficient, and more environmentally efficient. These developments place greater demands on engine lubricants.
A modern engine oil must therefore balance multiple requirements, including:
Friction reduction
Wear protection
Deposit control
Oxidation resistance
Thermal stability
Corrosion protection
Emission-system compatibility
Fuel economy
Component cleanliness
The correct combination of base oils and additives is essential to achieving the required performance.
Understanding Engine Oil Viscosity
Viscosity is one of the most important properties of engine oil.
Viscosity refers to an oil’s resistance to flow.
Oil viscosity changes with temperature:
Oil becomes thicker at lower temperatures.
Oil becomes thinner at higher temperatures.
Engine oil must flow sufficiently during startup while also maintaining an appropriate protective film when the engine reaches operating temperature.
Viscosity Index
The Viscosity Index (VI) indicates how much an oil’s viscosity changes as its temperature changes.
A higher VI generally means that the oil experiences a smaller change in viscosity across the measured temperature range.
Viscosity Index is traditionally determined using viscosity measurements at 40°C and 100°C.
Many synthetic and highly refined oils can provide a higher viscosity index than conventional mineral oils, depending on their formulation and base-oil technology.
SAE Viscosity Grades
The Society of Automotive Engineers (SAE) developed a standardized system for classifying lubricant viscosity.
Engine oils are classified under SAE J300, while automotive gear lubricants are classified under SAE J306.
SAE viscosity classifications address both low-temperature and high-temperature viscosity requirements.
Understanding Multigrade Engine Oils
Most modern automotive engine oils are multigrade oils.
A multigrade oil is designed to meet viscosity requirements at both low and high temperatures.
For example, in a 5W-30 engine oil:
5W represents the low-temperature viscosity classification.
30 represents the high-temperature viscosity classification.
The letter W stands for Winter and indicates the oil’s low-temperature performance classification.
Generally, a lower number before the W indicates better low-temperature flow characteristics.
The second number represents the oil’s high-temperature viscosity classification.
A higher second number generally indicates a higher viscosity at the specified high-temperature test conditions.
However, the higher viscosity grade is not automatically better. The correct grade depends on the engine manufacturer’s requirements.
High-Temperature / High-Shear Viscosity
Engine oils must also maintain suitable viscosity under severe operating conditions.
High-Temperature / High-Shear (HTHS) viscosity evaluates oil behavior under high-temperature and high-shear conditions similar to those experienced in highly stressed areas of an engine, including:
Bearings
Camshaft areas
Piston rings
Other highly loaded components
HTHS viscosity provides an indication of the lubricant’s ability to maintain an effective oil film under severe conditions.
An oil that becomes excessively thin under high-temperature and high-shear conditions may not provide the required protection for certain engine designs.
Viscosity Measurement
Different viscosity measurements are used depending on the test method.
Common units include:
Centistokes (cSt) – Used for kinematic viscosity.
Centipoise (cP) – Used for dynamic viscosity.
These measurements help characterize lubricant flow behavior under specified testing conditions.
Choosing the Correct Viscosity
The correct engine oil viscosity depends on the engine design, operating conditions, ambient temperature, and vehicle manufacturer’s requirements.
When selecting engine oil, always check the vehicle owner’s manual or official service information for the recommended:
SAE viscosity grade
API specification
ILSAC specification
ACEA specification
Manufacturer approvals
Using the correct viscosity helps ensure appropriate oil flow, lubrication, and engine protection.
How Is Gasoline Engine Oil Classified?
The American Petroleum Institute (API) has developed a classification system to identify engine oils according to their performance requirements.
For gasoline-powered passenger vehicles, the API S-Series is used to identify applicable service categories.
API S-Series
The API S-Series focuses on performance requirements for gasoline engine oils.
Depending on the category, requirements may address:
Piston deposit protection
Sludge control
Oxidation resistance
Wear protection
Turbocharger protection
Emission-control system compatibility
Fuel economy
Protection against abnormal combustion
Compatibility with modern fuels and engine technologies
As engine technology develops, new API categories may be introduced to address changing performance requirements.
API SN and SN Plus
API SN was introduced in October 2010 with requirements designed to provide improved protection for modern gasoline engines.
API SN addressed areas including:
High-temperature piston deposit protection
Sludge control
Seal compatibility
Oxidation performance
Emission-control system compatibility
Turbocharger protection
Fuel economy when applicable
Protection for engines using ethanol-containing fuels up to E85
API SN Plus was introduced in 2017 as a supplemental category, particularly addressing concerns related to Low-Speed Pre-Ignition (LSPI) in certain modern turbocharged gasoline engines.
The supplemental requirements included additional testing intended to evaluate protection against LSPI.
API Testing and Licensing
Engine oils claiming API licensing must meet the applicable performance requirements and testing criteria.
Testing can evaluate areas such as:
Wear protection
Deposit control
Sludge control
Oxidation resistance
Piston cleanliness
Turbocharger protection
Fuel economy
Emission-system compatibility
Abnormal combustion protection
API licensing provides a standardized framework for identifying oils that meet specified performance requirements.
What Is ILSAC?
ILSAC, the International Lubricant Specification Advisory Council, is an organization involving automobile manufacturers from the United States and Japan.
ILSAC develops gasoline engine oil specifications addressing areas such as:
Engine protection
Fuel economy
Deposit control
Emission-system compatibility
Turbocharger protection
Oil performance
Compatibility with modern fuels and engine technologies
ILSAC specifications are closely associated with API gasoline engine oil categories.
ILSAC GF-5
ILSAC GF-5 was introduced in October 2010 and established performance requirements for gasoline engine oils.
The specification focused on:
High-temperature piston deposit protection
Turbocharger protection
Sludge control
Improved fuel economy
Emission-control system compatibility
Seal compatibility
Protection for engines operating with ethanol-containing fuels up to E85
ILSAC specifications are periodically updated as vehicle and engine technologies develop.
API and ILSAC Specifications
API and ILSAC specifications are closely related but serve different roles.
API provides service categories and licensing requirements, while ILSAC develops specifications focused primarily on gasoline engine oil performance requirements established by participating automobile manufacturers.
Many gasoline engine oils carry both API and ILSAC designations when they meet the applicable requirements.
When selecting an engine oil, always verify the specification required by the vehicle manufacturer.
Resource Conserving
Resource Conserving is an API supplemental designation for certain gasoline engine oils.
It replaced the earlier Energy Conserving designation and expanded the focus beyond fuel economy alone.
Resource Conserving requirements address areas such as:
Fuel economy
Emission-system protection
Turbocharger protection
Engine cleanliness
Compatibility with specified ethanol-containing fuels
Overall engine protection
The objective is to provide an appropriate balance between fuel-efficiency performance and engine protection.
Selecting the Right Engine Oil
Choosing the correct engine oil requires more than simply selecting a viscosity grade.
Consider the following:
SAE Viscosity Grade – Use the viscosity recommended by the vehicle manufacturer.
API Category – Confirm the required API performance category.
ILSAC Specification – Where applicable, verify the required ILSAC specification.
Manufacturer Approvals – Check for specific manufacturer approvals.
Engine Technology – Consider turbocharged, direct-injection, hybrid, and other modern engine technologies.
Operating Conditions – Consider climate, driving conditions, engine load, and service requirements.
Ignitol Engine Oils
Ignitol Engine Oils are formulated to provide effective lubrication, engine cleanliness, wear protection, and reliable performance across a range of operating conditions.
The correct combination of base oils and performance additives helps support essential functions such as friction reduction, deposit control, cooling, sealing, corrosion protection, and component protection.
Ignitol Engine Oils are available in different viscosity grades and performance specifications to meet the requirements of various petrol and diesel engine applications.
To Conclude
Modern engine oils perform many essential functions beyond simple lubrication. They reduce friction, control deposits, transfer heat, support sealing, dampen mechanical shock, protect against corrosion, and can transfer hydraulic energy within modern engine systems.
Understanding viscosity, SAE grades, API classifications, ILSAC specifications, and additive technology can help vehicle owners make better-informed decisions when selecting engine oil.
However, the most important consideration is always to use an engine oil that meets the vehicle manufacturer’s recommended viscosity grade and performance specifications.
The right engine oil helps provide the lubrication, protection, cleanliness, and performance required by today’s increasingly advanced engines.
