It could only be “designed” thin out within the limits of the approval’s viscosity retention requirements (which would be the same for any oil).I always thought that M1 FS 0W-40 was designed this way. It's the "fuel efficiency" motor oil in the entire FS lineup. Way back when, Mobil used to advertise it as fuel efficient motor oil. In fact, today they advertise Mobil 1 ESP X3 0W-40 as being more fuel efficient than Mobil 1 ESP 5W-30. Go figure...
It would also be an odd design feature since all fuel economy/CO2 emission testing is performed with new oil. It isn’t a benefit if the oil mechanically shears later on.
And anyway I don’t think mechanical shear of the VM is as prevalent as some people think it to be, most viscosity deviations seen here are likely fuel dilution.
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