Most people are aware that while oils are compatible, many use different detergent/additive systems and should not be mixed. It is best to stay within the same brand when possible.
It does not hurt if you switch brands often, or occasionally mix in different brands, but you're not getting an optimal oil and you are only getting an uknown.
The case for improving VI falls along the same line of thinking.
"When you mix golf balls and basketballs, you don't get softball sized spheres - you get a physical (not chemical), mixture of golf balls & basketballs. When you mix a low molecular weight oil with a high molecular weight oil you get a physical mixture with molecules of different sizes. The extreme temp properties of those mixtures can't be determined "a priori" (theoretically), only by experiment." - TS
It does not hurt if you switch brands often, or occasionally mix in different brands, but you're not getting an optimal oil and you are only getting an uknown.
The case for improving VI falls along the same line of thinking.
"When you mix golf balls and basketballs, you don't get softball sized spheres - you get a physical (not chemical), mixture of golf balls & basketballs. When you mix a low molecular weight oil with a high molecular weight oil you get a physical mixture with molecules of different sizes. The extreme temp properties of those mixtures can't be determined "a priori" (theoretically), only by experiment." - TS