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Difference between API SL & SM

The differences as published by the API are as follows:

SM is limited to .06 min/.08 max percent phosphorous.
SL is limited to .10% max phosphorous.

TEOST is limited to 35mg max for SM
TEOST is not rated of SL.

Sulfur is .5% max (0w/5w) for SM
Sulfur is .7% max (10w) for SM

Sulfur is not limited for SL.

Engine test for SM is sequence IIIG
Engine test for SL is sequence IIIF

SM limits viscosity increase to 150% max at 100 hours.
SL limits viscosity increase to 275% max at 80 hours.

Cam wear using sequence 4A limited to 90 micron max for SM.
Cam wear using sequence 4A limited to 120 micron max for SL.

Bearing weight loss using sequence 8 is 26 mg max for SM.
Bearing weight loss using sequence 8 is 26.4 mg max for SL.

There are numerous other differences but they are measured using different test sequences and therefore not directly comparable.

According to American Petroleum Institute's (API) Engine Oil Licensing and Certification System,

- The Valve Train Wear, or known as average cam wear under engine Sequence IVA Test (ASTM D6891);

1) API SJ (for 2001 or older gasoline engine) and API SL (for 2004 and older gasoline engine) specify not more than 120 micron of wear, comparing with;

2) API SM (for 2010 or older gasoline engine) and API SN (current) specify not more than 90 micron of wear....

Even though newer API standards call for lower phosphorus content (anti wear agent) due to catalytic converter preservation, It does not allow more wear to take place, especially valve train wear.... With the help of new additive technology, API SN and SM must resist wear better than API SJ and SL which has higher content of phosphorus as anti wear agent...

For your infomation, current additive technology has enable the cam wear to be reduced down to 30 micron.


Number of modern car models have ECU that monitor the functionality of the catalytic converters, early poisoning of catalytic converters will be a bad news.... some car ECU will respond by cutting power output...

However, eventhough with less anti wear agent, latest API SM and SN standards control average cam wear (sequence IVA) and allow maximum 90 micron (1/1000mm) of wear, whereas, in older standard, such as API SL and SJ, they allow maximum waer of 120 micron..... 
You must understand the phosphorus level will deplete during operation, but API SN with Resource Conserving and ILSAC GF-5 would require the engine oil to retain minimum 79% of phosphorus during test.

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