0W would be better at startup. If the car has any sort of noises at startup, usually by going 0W would reduce it significantlyOriginally Posted by HoldenAstra
40 would be quieter. When the engine has reached its operating temperature, 40 is thicker than 30, therefore absorb internal engine noise better
40 is thicker, so it should be protecting more.
30 would be lighter to rev. If you like revving or accelerate hard, 30 would be better.
I personally wouldn't play with the Viscosity at operating temperature. If manufacturer recommends, say, 15W-40, I would try anything x(<15)W-40, but never different than it, unless looking for acceleration performance like previous paragraph.
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