Technically 10W30 can. Our engine using 3.7 liters of EO. So buying 3 liter pack will be a problem to refill sufficiently isn't it?

If you're using 40 rated all this while, changing to W30 might makan minyak coz your engine, piston, etc already sync and used to thicker lube. 2ndly campro iafm excel in mid to high speed runs. If you constantly do runs over 100km/h, with out hot engine and existing cooling system, W40 will be more suitable.

If you run W30 from the beginning then ok. Also without any reference, IMO, some of the reasons W40 was used as default for PE might be due to 2 things.

1. Outdated recommendation. (manual even recommend W50 that is rarely used for new cars at this range anymore).

2. Hot engine with existing cooling system. Our campro IAFM is not an exact duplicate (I believe only, no fact), of the newer Preve IAFM, so our engine might tends to runs a big hotter. w30 although suitable for city drive, does not do very well in higher speed highway runs in our engine. Newer engine with better flow efficiency, tighter tolerance and better cooling system got not problem with that tho..