guys , what's the difference between liqui moly toptec ? synthoil  ? molygen ? they are all fully synthetic oil , right ? I'm looking for fully synthetic oil now for my persona ... Or any brand suggestion for fully synthetic oil ? I have been using shell helix semi synthetic all this while , i can feel the engine sound is quite rough

Btw, for engine oil, the best choice is Petronas Syntium 800 10W-40 (Synthetic blend).
This is the engine oil recommended by Proton. It may be slightly thick but it suits the Campro engine. 

I am using shell helix semi now, can feel that the engine is quite light, but sound rough.....

campro engine roar is loud as they want to mimic sport cars ala Lotus Gen2 (1st campro engine car). There's no engine oil can reduce as much as 10dB, except do loads of soundproofing

Haha ok its up to you lor, coz its your money anyway. Using such expensive oil on your engine is actually a waste of money, just like using RON 97 on a Myvi for example. Also if you buy from reputable sellers, it will be genuine oil. Liqui Moly also only sold in independent workshops so there's no guarantee they don't sell fakes. If you really want to spend that much though, might as well buy Amsoil, more proven. Price might be slightly cheaper but maybe a bit more difficult to find.

Untuk shiok sendiri, have a read.

I am wondering 5w40 suitable for my car or not... The manual stated 10w30 btw.... Some ppl advice me to use xw40 as I travel highway quite often.....

strange, that manual must be from Campro CPS variant, as that time CPS engine oil recommended 10W30 while legacy Campro specify 20W50.

Dunno oh, it's persona manual btw

is yours Persona SV (Sacrificed Value)? Maybe later batch they just share same engine oil spec in manual with CPS CFE variant

Bro the engine is the least of your worries, the engine is normally the most robust part of the car... just use any good oil and follow proper maintenance is ok already.
It's the other parts connected to the engine which most likely kaput first.

To me the cooling system is more important than the engine oil..  engine can run even if oil leaking... but coolant leaking, bye-bye engine.

My cars are 13 years and 8 years old respectively, no worries on the engine.. other parts hard to say, see luck.

So what is the suitable oil spec? 😂

That car engine does't need expensive full synth oil like Liqui Moly. Just buy whatever branded full synth on promotion in Giant/Tesco/AEON like Shell/Castrol/Mobil/Mitsu Eneos, more than enough.

i can feel the engine sound is quite rough

All new Protons are filled with 100% coolant in the radiator before they leave the factory.
For best results you should only refill 100% coolant. Do not dilute with distilled water, etc.

There is no need to flush the radiator too often. (Just do it once every 5 years or 60k km whichever comes first)
As a rule of thumb, just flush the radiator when you change the timing belt/water pump.
Btw, you will need many bottles of coolant for this. Around 4-5 bottles I think. 

Otherwise, just top up the coolant (if necessary) during the regular scheduled service.