Engine Oil Specifications: JASO Explained

JASO (Japanese Automotive Standards Organisation) in essence is a Japanese version of the API engine oil classification.


Although API is commonly used in the Japanese market, Japanese engine manufacturers felt the need to develop their own engine oil specifications tailored to meet requirements of their engine designs more specifically. Although JASO has classifications for light and heavy-duty diesel engine oils, they are globally known for their small engine oil classifications and small engine manufacturers all over the world adopted the JASO standards to make recommendations on oils to use in their engines.


JASO developed three categories of engine oils:

1. Light and heavy-duty diesel engines,

2. Small four-stroke petrol engines,

3. Small two-stroke petrol engines.


The JASO classification for diesel engines can be identified by the letter “D” and will be followed by a second letter, “H” for heavy-duty diesel engines or “L” for light-duty diesel engines. The combination of two letters will then be followed by a number which indicates the specification level.

Oils in this category have to pass valve train wear, soot handling, evaporation oil loss, piston cleanliness and foaming deterioration tests to meet the requirements.

The two-stroke petrol engine oil specification can be identified by the letter “F” and will be followed by a second letter indicating the performance level. The further along the letter is in the alphabet, the higher the performance level. Oils in this category have to pass detergency, lubricity, initial torque and smoking tests from manufacturers like Suzuki and Honda to meet the specification requirements.

The four-stroke petrol engine oil specification can be identified by the letter “M” followed by a second letter indicating the performance level. The further along the letter is in the alphabet, the higher the performance level. In addition to standard small engine performance requirements, these oils also undergo numerous wet clutch performance tests.



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Phone: +27 021 410 8720

Written By Henco Booysen


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