It comes down to tolerances. Machining is much more precise. Too thick an oil is just as bad as too thin an oil. I figure the engineers designing the engine know their stuff do I run what they recommend which mean some of my cars get 10w30 or 10w40 and others 5w20 or 0w20.I always thought that if at all possible, it was best to pick an oil that had the lowest viscosity range that met your application. Because the modifiers that were added to achieve the viscosity range came with their own problems (longevity?). So a 5w30 probably has more of those modifiers than 10w30, and to me would be far less desirable to use.
For no longer than an engine is off during a stop/start incident, any regular oil is still going to be clinging to the components that need lubrication.Speaking of Castrol oil, is anyone using Castrol Magnatec? It's like 2 or 3 times the price of I guess regular Castrol. Supposed to "stick" to metal for when the engine isin't running, less wear for when the engine starts up.
But interestingly enough, a marketing angle like that doesn't seem to be aimed at the new-fangled way that the crazy new cars are operating (ie - shutting down the engine when you come to a stop, like at a red light). Which got me wondering if any oil company is thinking about making an oil for this new operating mode, if there are any technical or chemical reasons for a special formulation.
Seemed like an unnecessary gimmick to me. Like you say, unless the car is sitting for extended periods, generally any old oil will still be in the top endFor no longer than an engine is off during a stop/start incident, any regular oil is still going to be clinging to the components that need lubrication.