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What You Need to Know Part 2
In part 1 we talked about what motor oil is made of, base stock and additives. Today we will talk about 7 functions or “jobs” a motor oil has inside your engine.
What must a motor oil do?
Modern motor oils are highly specialized products carefully developed by engineers and chemists to perform many essential functions. The additives in a motor oil are what give it its qualities to help with its performance. The jobs a motor oil must do are: friction reducer, cleaning, cooling, lessen shock on parts, prevent rust, and seal the combustion chamber
Minimize Friction
Lubricants reduce contact between components, minimizing friction and wear. They accomplish this by leaving a thin film on the surfaces of parts. The ability of an oil to remain “stuck” to a part and coating it after long periods of “sitting still” is a major preventer of wear during a “cold start”. A “cold start” refers not just to cold temps, but also refers to engines that haven’t been started in a while, like overnight. Studies have shown that cold starts are where most engine damage occurs.
Cleaning power
Lubricants maintain internal cleanliness by suspending contaminants within the fluid or by preventing the contaminants from adhering to components. Base oils possess a varying degree of solvency that assists in maintaining internal cleanliness. Solvency is the ability of a fluid to dissolve a solid, liquid or gas.
The place where oil works hard.
While the solvency of the oil is important, detergents and dispersants play a key role. Detergents are additives that prevent contaminants from adhering to components, especially hot components such as pistons or piston rings. Dispersants are additives that keep contaminants suspended in the fluid. Dispersants act as a solvent, helping the oil maintain cleanliness and prevent sludge formation.
Cooling
Reducing friction minimizes heat in moving parts, which lowers the overall operating temperature of the equipment. Lubricants also absorb heat from contact surface areas and transport it to a location to be safely dispersed, such as the oil sump.
Fun Fact: Lubricating an engine requires a very small amount of motor oil compared to the amount needed to ensure proper cooling of all these internal parts.
Seal
Motor oil acts as a dynamic seal in locations like the piston ring/cylinder interface. A dynamic seal helps keep combustion gases in the combustion chamber, which maximizes horsepower and helps prevent hot gases from contaminating the motor oil in the sump.
Dampen Shock
A lubricant can cushion the blow of mechanical shock. A highly functional lubricant film can resist rupture and absorb and disperse these energy spikes over a broad contact area. As the mechanical shock to components is dampened, wear and damaging forces are minimized, extending the component’s overall operating life.
Protect Against Corrosion
A lubricant must have the ability to prevent or minimize internal component corrosion. Lubricants accomplish this either by chemically neutralizing corrosive products or by forming a barrier between the components and the corrosive material.
Fun Fact: Motor oil has no natural ability to resist rust and corrosion; those properties must be added through use of motor oil additives.
Transfer Energy
Because motor oil is incompressible, it makes an excellent energy-transfer medium, such as when used with hydraulic valve lifters or to actualize components in an engine with variable valve timing.
As you can see, modern motor oils have many functions or “jobs” they must complete, especially as todays engines become smaller, produce more horsepower, increase fuel mileage and help reduce emissions. These goals all increase the workload of motor oils and producing an oil that accomplishes all these tasks takes time and testing to get the right balance. However, the correct balance of additives will help your motor oil protect your engine and make it last longer.
What is viscosity?
Viscosity refers to the oil’s resistance to flow and is the most important property of an oil. The viscosity of oil varies with changes in temperature – thinner when hot, thicker when cold. Although oil must flow at cold temperatures to lubricate the engine at startup, it must also remain thick enough to protect the engine at high operating temperatures. When an oil is used at a variety of temperatures, as with most engines, the change in viscosity should be as minimal as possible.
Wouldn’t it be handy to have a number that indicated the oil’s viscosity change? We do, and it’s called the Viscosity Index (VI). It is measured by comparing the viscosity of the oil at 40°C (104°F) with its viscosity at 100°C (212°F). The higher the VI, the less viscosity changes with temperature changes, and the better the oil protects the engine. Synthetics typically have a higher VI than conventional oils.
SAE viscosity grades
For engine and gear oils according to the SAE standards J 300 and J 306
SAE stands for Society of Automotive Engineers. The SAE developed a classification system to define the viscosity or thickness of oil. This system has been progressively modified over the years. It defines “operating temperature” engine oil viscosities for different grades and contains specifications for “cranking” viscosity and pumpability at start up, the “W” grades or winter. A multigrade oil is one that meets both a “W” low temperature viscosity requirement and a 100°C “operating temperature” requirement. The classifications increase numerically; the lower the number, the lower the temperature at which the oil can be used for safe and effective engine protection. Higher numbers reflect better protection for high-heat and high-load situations
For engine oils there is a specification that must be met at 150°C, known as a High Temperature/High Shear (HT/HS) viscosity. HT/HS simulates what happens in high stress areas of the engine e.g. bearings, cams, etc. It measures the viscosity and indicates the oil film thickness under severe high-speed conditions. An oil that is too thin under these conditions may not provide the required protection to prevent significant wear in these critical engine parts.
Centipoise (cP) and Centistokes (cSt) are the units viscosity is measured in. The following chart shows a comparison of different viscosity grades versus temperature rang.
Understanding Viscosities
The number in front of the “W” signifies the viscosity of the oil at cold/start up temperature (tested at -10 to -35°C depending on the grade. Please refer to the SAE J300 – Engine Oils Chart opposite). The lower the first number, the faster the oil flows (pumpability) when the engine is cold. The second number represents the oil’s thickness at operating temperature (100°C). All oils thin out as they get hotter. So, the higher the second number, the less the oil will thin out as it heats up, compared to an oil with a lower second number. Normally, multigrade viscosities are measured on a curve.
In the example above, all three oils have the same operating temperature viscosity but different cold temperature viscosities. All three will be similar viscosities when at operating temperature, measured at 100°C In the example below, all 4 oils gave the same cold temperature viscosity, but different operating temperature viscosities.
The next graph shows the differences between three different multigrade oils
The overwhelming majority of oils today are multi-viscosity, meaning they behave differently at different operating temperatures to provide the best of both worlds – good cold-flow when the temperature drops and reliable protection once the engine reaches operating temperature. For example, a 5W-30 motor oil performs like an SAE 5W at 40ºC and an SAE 30 motor oil at 100ºC.
With all these choices of oil, its best that you consult your owner’s manual for the proper oil viscosity. Some manufactures recommend a summer viscosity and then a different winter viscosity based on the temperatures in your area.
The Society of Automotive Engineers (SAE) set parameters for multigrade oils and viscosities base upon cold cranking viscosity, pumpability and cST measured at operating temperature. The table below shows these requirements.
How is gasoline motor oil classified?
The American Petroleum Institute (API) developed a classification system to identify oils formulated to meet the different operating requirements of gasoline and diesel engines. The API system has two general categories: Series and C-series.
S-series service classification for passenger vehicles
API S – Series
The API’s S-series classification system focuses on creating standards for oils with properties that are critical to modern gasoline engines. The latest Standard, SN+, focus on improving the following items from previous standards (API SM): protections for pistons from deposit, improved oxidation resistance, improved performance with emissions systems, maximizing fuel mileage, preventing LSPI or super knock.
An oil must pass a series of bench tests and engine performance tests (API Sequence tests) to be licensed by the API and to use the API starburst.
The classifications increase in alphabetical order as the performance standards for motor oil are increased for new engine technology or when issues pop up unexpectedly. This was the case for the increase from SN to SN+ in 2017, due to LSPI damage to pistons and instituting a LSPI prevention test. Each new classification replaces the previous classification. These new classifications are “usually” backwards compatible, meaning they meet the performance requirements of previous standards and may be used in engines requiring the older standards. The new FA4 oils for newer (2017 and newer) over the road diesels is an example of a non-backwards compatible oil classification.
Here is the API standard for the SN classification from the API site:
“Introduced in October 2010, designed to provide improved high temperature deposit protection for pistons, more stringent sludge control, and seal compatibility. API SN with Resource Conserving matches ILSAC GF-5 by combining API SN performance with improved fuel economy, turbocharger protection, emission control system compatibility, and protection of engines operating on ethanol-containing fuels up to E85.”
The + was added to the SN classification in 2017, at the demand of auto makers, because LSPI was such a major issue in newer engines. The + supplemental added the LSPI prevention test.
What is ILSAC?
ILSAC is a committee made up of US and Japanese auto makers. They recommend oils that are API licensed for use in vehicles. This committee does not have standards for vehicles before 1993. However, the most current standard (GF-5) contains the performance properties of all prior standards and these oils are recommended for use in older engines as previously recommended.
Here is the current ILSAC standard, ILSAC GF-5.
This is the definition is from ILSAC itself. “GF-5 – Introduced in October 2010, designed to provide improved high temperature deposit protection for pistons and turbochargers, more stringent sludge control, improved fuel economy, enhanced emission control system compatibility, seal compatibility, and protection of engines operating on ethanol-containing fuels up to E85.”
You’ll notice that the API and ILSAC classifications almost are identical. That’s because the oils that ILSAC recommends are API-licensed. And API standards are based on the need of engine protection from automakers. To answer another question, yes there are oils produced that don’t meet these standards. So you need to be careful when buying oils. API is now posting on their website the oils that are illegally using their “starburst”. Those are the oils that have not passed the test to use the symbols.
Some things you should keep in mind about these standards are: They are industry minimum requirements for oils and Oil manufacturers must pay for API licensing of the oils
Resource Conserving – What does it mean?
In 2010, the API introduced a new supplemental category for motor oils called resource-conserving. This replaced the energy-conserving category, which only focused on the fuel-saving properties of oils. Resource-conserving oils now include properties focused on: emissions system protection, Turbo protection, Compatibility with ethanol fuels up to E85, Along with maximizing fuel savings.
Thank you for having interest of reading our article.