not necessarily true.
Mixing differing brands is like mixing chemicals. It can have bad results.
All oil is designed for differing purposes. Many oils of the same weights from differing brands will have obviously come from the very same well.
so how can they be different?
The brands will buy the same oils but add their differing chemicals offering differing properties. For example they may contain anti foaming agents, long life properties, anti wear properties etc. some oils are for high milage cars others are for race engines and track cars.
zinc dialkyldithiophosphate offers metal on metal protection. the last barrier of protection in high reving or turbo applications. this can be directly effected by certain chemicals.
Brands use naphthalene, xylene, acetone and isopropanol for detergents to clean deposits. These detergents do the oposite of zincdialky.....phate. they strip and clean, not stick and lube.
How much detergent is needed in an oil? what if the oil your about to pour in to top up has more than the one in your engine with is full of the metal on metal protecting zinc? how do you know there is not so much detergent that the boundry protection layer is not breached?
some of the oil additive products actually are capable of producing less engine friction, better gas mileage and higher horsepower out put. this is reduced protection comes at the cost of changing the oil more frequently. but it increases performance. it will denature quicker. ie a race car will change its oil after every race to prolong the engine life as the oil cant protect for long.
im a huge believer in the "look after oil and it looks after your car". i use good oil and change it regulary. but i believe most oils are all the same they just have differing chemicals offering differing things... so just choose what performance you need, stick to the one type for your cars life and change it very regular!!
