Is there really any difference between HM and SN rated motor oil besides the marketing?
Yep.
High mileage oils are just that. They can have elevated levels of zddp which makes them unable to meet the SN classification and from what I've seen usually meet the outdated SL spec.
High mileage oils can be formulated to meet various spec's,SN is the latest API classification.
Is there really any difference between HM and SN rated motor oil besides the marketing?
HM and SN are not mutually exclusive. There are SN HM oils and even a few SN/GF-5 ones. These can even be used in brand new cars where SN is the primary spec.
Originally Posted By: wemay
If you are looking for a HM SN in xw30, there are some:
Maxlife - SN /GF5
Maxlife syn - SN / GF5
GTX HM - SN/GF5
MS5K HM - SN/GF5
PNZL HM - SN