API CJ-4/SN vs API CJ-4/SN/SM

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Hello,

What is the main difference between API CJ-4/SN and API CJ-4/SN/SM ?

SN - its the most recent spec for oil. Can it be used in all gas engine, any year?
SN/SM - Why some oil are rated SN and SM ?

I want to used Amsoil API CJ-4/SN in a 2002 gaz engine ,should it be ok ?
thanks
 
What is the main difference between API CJ-4/SN and API CJ-4/SN/SM ?

Oil marketers cannot put two API S categories in the donut. However some do put a reference to older categories (API SM) in their technical data. The differences between SN and SM can be viewed in the API 1509 Appendix G (Table G4 and G5)

SN - its the most recent spec for oil. Can it be used in all gas engine, any year?

Yes. API SN oils are considered backwards compatible (provided you use the correct viscosity grade as specified by your OEM)

SN/SM - Why some oil are rated SN and SM ?

This depends on the date of production or sometimes the new requirements (such as phosphorus limits) disqualify the oil from claiming the most recent category. Manufacturers are able to claim any of the current specs including: SN, SM, SL, SJ, SH (when used as described in API 1509 7.3.3), CH-4, CI-4, and CJ-4.

I want to used Amsoil API CJ-4/SN in a 2002 gaz engine ,should it be ok ?

Yes it should be ok. Are you using the grade specified in your OEM. Note sometimes you will have higher phosphorus (in the form of zddp) in CJ-4 rated oils - especially 15W40. This is because the typical limit of 800ppm is only required for SAE 0W-16, SAE 5W-16, SAE 0W-20, SAE 5W-20, SAE 0W-30, SAE 5W-30 & SAE 10W-30 (all other SAE grades are not require to report phosphorus content). In the case of the Amsoil products both their 10W30 and 15W40 products are licensed and meet the requisite performance categories for API SN
 
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