break in oil and changes

roylerumble said

correct me if Im wrong, but isn't a multi viscosity oil like 5w 20 or 10w 30 suitable for multi temperatures and the 5w or 10w refers to the cold weather viscosity, lower the W number the thinner at cold temps? So SAE 30 would be the same at any temp? And break in oil has zinc and phosphorus addivitves for break in. Or is there a difference between conventional oil and break in oils....?

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The issue is cold start and actual operating temp oil viscosity.

The oil will act like the winter grade number on start up and when at operating temp it will act like a 30. A 30 will be like a 30 on cold start and get thinner with temp.

The reason for single grade oils is that before WWII is that Viscosity Index Improvers were pretty rare, and what was available was sketchy at best. After the war, the VI Improvers because better and now are damn near fool proof. I say damn near because I've seen guys use oils with alcohol that weren't alcohol compatible and the results were bad at best.