Have you ever wondered what that “SAE” on the bottle of your motor oil means?
You’ll see these three letters on most brands of motor oil, right before the viscosity grade. And if you don’t, you might want to skip that motor oil!
So, what is SAE oil?
And what does the SAE oil number indicate?
We’ll do our best to explain all this, and we’ll also get into interpreting the SAE oil number and answer some FAQs you might have about SAE oil.
Let’s get started.
An SAE oil is a motor oil that complies with the SAE standard.
What’s that?
Motor oils are classified by viscosity, using a rating system developed by the SAE (Society of Automotive Engineers).
The letters “SAE” should precede the oil viscosity on the motor oil labeling. If it doesn’t, the oil might not be compliant with the SAE viscosity grade.
This means that if your engine manufacturer recommends “SAE 10W-30,” one labeled as just “10W30” might not meet the viscosity characteristics of the recommended oil.
Now that you know what SAE oil is, let’s understand the SAE oil number.
The SAE number (also known as “viscosity rating” or “viscosity grade”) is a code to grade motor oils by their viscosity characteristics.
The SAE viscosity grade is not the actual viscosity value of the motor oil.
Originally, viscosity ratings were monograde — meaning it was only one number (like engine oil SAE 30). Multigrade oils were introduced in the 1950s to address varying engine operating conditions and temperature issues.
Use of engine oil additives, called viscosity index improvers (VII), allowed oils to thin at a slower rate, retaining a higher viscosity index even at a higher temperature.
So how does this help, exactly?
Remember that your engine heats up with use and may be influenced by the external temperature as seasons change.
Multigrade oils can perform at a wider operating temperature range.
Engine oil grades like SAE 5W-30 or 10W-40 are commonly used (for both gasoline engines or a diesel engine) because they’re thin enough to flow at a low temperature but thick enough to perform well at a higher temperature.
This means that your engine can generally use the same oil as summer switches to winter.
So how do you read the SAE oil number?
Multigrade oils have two numbers, in the format “XW-XX.”
The SAE J300 standard defines these numbers individually for monograde oils.
Any multigrade oil must pass the SAE J300 viscosity grade standards to be approved for use.
So, these two numbers — what do they indicate?
The first digit indicates how well the oil flows at 0oF. The letter “W” is for “Winter.”
The lower this number is, the less likely the motor oil will thicken at lower temperatures.
In cold temperature regions, 0W or 5W oils tend to work best.
This number indicates the oil viscosity rating at an operating temperature of 212oF. It shows how fast the motor oil thins and is crucial to proper engine lubrication and protection at a high temperature.
The higher this number is, the better the oil performs at increased ambient temperature.
If the engine heats up beyond a certain temperature threshold, the motor oil will experience thermal breakdown and start to degrade.
Let’s see how these oil grades work for a clearer picture.
First, check what motor oil your engine manufacturer recommends.
SAE 5W-30 is a very common engine oil for cars and light trucks.
But let’s say it isn’t available.
What do you do?
You’ll need to find an oil based on your driving conditions. For example:
In low temperature zones:
In high temperature areas:
Note: The SAE has a separate viscosity rating system (SAE J306) for axle, gear, and manual transmission oils. These shouldn’t be confused with engine oil viscosity grades. A high gear oil number (like 75W-140) doesn’t mean it has a higher viscosity than motor oil.
We’ve got the basics of SAE oil down.
Let’s go over some FAQs next.
Here are the answers to some questions you might have:
The Society of Automotive Engineers (SAE) was founded in 1905 by Henry Ford and Andrew Ricker.
SAE standards oversee the automotive industry and play a part in petroleum, aerospace, trucking industries, etc. Its primary purpose is to ensure consistency across markets and is responsible for designing the viscosity grading system for motor oils.
This means any SAE oil you bought in the US would be the same as one in Japan. If these standards weren’t in place, motor oil would vary everywhere, and prices would rise.
Viscosity describes the resistance of a fluid to flow.
A higher viscosity (thicker) oil takes longer to flow than a lower viscosity (thinner) oil, and heat directly impacts engine oil viscosity.
Thermal breakdown can happen when the engine gets too hot and changes the oil’s viscosity.
The viscosity change will cause decreased oil flow, which may eventually lead to deposit buildup, damage to the engine’s metal surfaces, and increased oil consumption.
SAE oils can be synthetic or otherwise.
Having the SAE designation simply means it complies with the SAE standard.
An SAE oil can be regular oil (conventional oil) or other types of engine oil (like synthetic motor oil).
An SAE prefix simply means that the oil meets the SAE standard.
Monograde oils only have 1 grade (like SAE 30 or 20W) as defined by the SAE J300 standard. They’re also called “straight-weight” oils.
The SAE J300 has 11 viscosity grades established, 6 of which are “winter” grades with the “W” suffix. An SAE J300 monograde oil can’t use polymeric viscosity index improver additives.
So, when is a monograde oil a better option than multigrade oils?
You might want to use a monograde oil in regions or seasons with extreme temperatures.
Say you drive in desert heat all the time; a monograde oil might make more sense to cope with a scorching ambient temperature.
Motor oil isn’t just a lubricant to reduce friction between moving parts, preventing engine wear. It also contributes to fuel economy, emissions controls, and engine design advancements.
The ILSAC GF-6 is the newest ILSAC motor oil standard, introduced in May 2020. It’s aimed at improved fuel economy and enhanced passenger car engine capabilities, providing low-speed pre-ignition (LSPI) and timing chain wear protection.
The GF-6 standard replaces ILSAC GF 5 and is backward compatible with previous generations.
Engine lubricant can generally be divided into these four types:
