i think we must stick on company recommendation regarding Viscosity of the Oil , which is 5w30 which is thinner than 5W40 , which gives even better fuel economy than 5w40 not only fuel economy but its also good for the total life span of the engine. you should go to thicker Viscosity if your Car consumes Oil which is a very long journey if you use good and high quality Lubes, but you must not go straight from 5W30 to 5W40 , there are certain step to change the viscosity for the long lif e of the Engine.
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