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For one of my cars in the recommended oil it says 'Use API sj, sl or above' and for my other older car(99) it says use 'api sg, sh, or sj' but doesn't say above.

Based on what I have seen it seems API codes always supersede the previous codes so am I correct in thinking that you can always use api s codes that are during or after your vehicle and therefore it is fine to use API SN, SM, SL etc in my second vehicle?

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  • Not necessarily. Some of the newer grades have lower limits for some of the more effective additives, as these while good for the engine could impact catalytic converter life. Hence a newer spec oil might not be as effective a lubricant for an older vehicle.
    – Kickstart
    Commented Oct 7, 2019 at 12:21

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In this series ( S ) of API oil codes , the lower down the alphabet ,apparently the more severe the testing criteria. So an oil rated SN can pass the tests for all the other ratings.( As I remember this was not always the case in previous API oil service codes. ).

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A friend in the oil industry wrote a nice guide for me a while back which may help, it's here:

http://fuddymuckers.co.uk/wiki/doku.php?id=tech:oil:acea

Relevant section:

API ones are easy. Anything starting with an S means Spark, anything with a C means compression, so therefore gasoline and diesel respectively. Then with each generation of spec they have gone a letter higher in the alphabet, but retain back-compatibility to anything that has gone before it.

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