Thanks! Let me rephrase,I got no problem with the "cold" viscosity ... the only experiment in this regard I've made it was in the Ct200h wifemobile, which once I failed to secure the recommended 0W-20 and found 5W-30 and on startup/initial cold running the engine was noticeably rougher. So I am with you on the cold concept ..... My concern is, as explained, at high temp/high load. Don't know you guys, but except a brief spell, it has been every day around 30 Celsius since mid-June. This puts you in the "tropical operating environment", and running on the highway at 2.4/2.7k RPM (that'd be 130/150 km/h) with a loaded car and AC on, I still believe puts a -30 to the edge of its limiting capabilities, true I seldom see past 110 in the instrument cluster indicator, but... Bear in mind all my other vehicles, albeit older, have always run on the various combinations 5W40 5W50 10W60 .... I am just not used to water for oil 😁😚 Lacking grounds to safely change - I do not know if I have the variable oil pump, for example, which to me also sounds folly - I might reduce replacement interval .... Thanks for bearing with me, feel free to simply write "stop thinking about it and DRIVE!" 😄