Normally for semi, I'll change every 5,000km - 7,000km and for fully synthetic, it'll be 10,000km - 12,000km. Anyway, I've only used semi synthetic no more than 5 times on all my cars as I always prefer full synthetic

It depends on which brand/type you buy. Normally it's RM100+ and some can be RM200+

Mobil 1 is a good oil I think it'll cost you RM180+ for a fully synthetic. If you want cheaper alternative, try BHP or Petronas.

Actually they are all more or less the same. I've tried so many brands - Motul, Mobil 1, BHP, Shell, etc and as long as it's fully synthetic, you get better performance and lesser engine noise compared to semi-syn. If you're onto track racing then maybe it'll be more of a difference but all of us are on street cars I just got 5 bottles of TORCO so I'll see how well it does.

I don't think that's true because the car engine itself plays a role in determining your service interval. BMW's can go 15K service cycle easily and Japanese makes are normally 5-10K. If we have the money then yes, can even change monthly but to optimize the investment, 10K change for fully synthetic seems to be reasonable. I do agree that "5,000km or 3 months whichever comes 1st" should apply for mineral oils

It is expensive I just wanted to try out and if I don't get a lot of difference, I'll switch back to something cheap.

You're right but unfortunately our Japanese make doesn't have a sensor like the Europeans so mileage is just a form of measurement used. You're on a Turbo engine so obviously it would be slightly different than most of us here (with a normal NA)

I think the problem is because some workshops workers/mechanics doesn't really know what engine oil viscosity is all about and their knowledge are mainly own assumptions instead of how things really work scientifically/technically

Google.com and it makes you understand many things from viscosity level to what fully/semi synthetic means