I want to share my experience of toyota Corolla GLI 2006.
That car was under my father possession. He dont know anything about engine oils.
He used the the all local brand oil (jo mechanic daal dy)
Zic A+
Zic A
Guard oil
Havoline
Shell
And he also used all available viscosity.
But he is very strict on changing oil at every 4000 km
When ever i try to convince him he said sub bakwaas ha sub oil aik jaisay ha marketing stunt ha.
His car is 3 lac plus km on odometer which run mostly on CNG.
When ever i drive his car i dont feel significantly difference in power as compared to my car.
Some time i wonder he may be right.