xw-30 vs sheared xw-40

[kr_bitog]

I read that many oils sheared to lower viscosity readily, however I am unclear what caused the oil shear and what oil properties diminishing beside the viscosity when it shears ?

The reason I ask is it seems many xw-30 GF-5 oil often makes engine sounds louder, so i am wondering if using xw-40 that shears readily will be better to achieve muted engine noise and compensate the power loss due to thicker oil compared with xw-30 oil ?
Please advise.
Thank you.

 

[CATERHAM]

Shear is not the problem it once was with modern oils today, particularly synthetic oils.

Personally I've never noticed an increase in engine noise running a lighter engine oil.
If you're really concerned that you're maintaining an adequate oil viscosity when the engine gets fully hot (and I'm sure you are) then install an oil pressure or even an oil temperature gauge.
Making a subjective accessment based on engine noise is not the way to go IMO.