a 20w50 has the same viscosity as a straight 40w. Look up mobile on the web and go to properties of
oil. The correct
oil is 10W30. If you want to impress people with saying you use "racing
oil" ,50wt, that is fine but in the depths of your garage put in 10W30 and you will not have a lubrication failure. 10W30 has the same viscosity as 20W at temperature. The greater the range of viscoity, like 20W50 is horrible because the additives (polymers) needed for that range are higher than say a 10w30. By the way the polymers take up volume in the oil but provide zero lubricating properties, so inside you little bearing you 75% oil and 25% mushy polymer.