Originally Posted By: TechnoLoGs
RP also makes a 0W-10.
Yes the non API RP XPR 0-10 is not any lighter than most 0W-20s due to it's low 140 VI.
Currently the lightest 0W-20 is Sustina (VI 229) followed I suspect by the Idemitsu made Mazda High Moly 0W-20 (VI 221).
When the new 0W/5W-16 grade becomes available it may not be any lighter than these two oils. The new grade can have a HTHSV as low as 2.3cP but need not, and the KV100 spec' can still as high as 8.2cSt.
There are plenty of 0W/5W-20 oils already on the market that could be relabeled as 16wt oils including the rather heavy RL 0W-20.