The Science Behind Engine Oils : What Do API and SAE Grades Really Mean?
When you’re choosing an engine oil, you’ve likely come across codes like API SN or SAE 20W-40. But what do these numbers and letters mean? Let’s break down the science behind these grades — and why they matter to your vehicle’s performance.
What is an API Grade?
API stands for the American Petroleum Institute, which sets performance standards for motor oils. API grades usually have two letters:
- S for Spark ignition (petrol engines)
- C for Compression ignition (diesel engines)
- API SN: Improved performance
- API SP: Latest spec for gasoline engines
What is an SAE Grade?
SAE stands for the Society of Automotive Engineers. It classifies oil based on viscosity, or how thick/thin it is at different temperatures. Example: SAE 20W-40
- 20W = Winter viscosity (how the oil behaves in cold)
- 40 = High-temperature viscosity (how it protects your engine when hot)
Why It Matters
Using the correct API and SAE grade ensures:
- Proper lubrication in all temperatures
- Reduced engine wear
- Better fuel efficiency
- Long engine life