How frequent change Persona Coolant & Plug?

How frequent change Proton Persona's plug?

20k， major service换
如果要经济可以用platinium plug (bosch super 4),
40k才换

How frequent change coolant?

coolant通常SC是20k换一次（和brake fluid一样）
我用着toyota coolant
如果要效果不错，可以用nissan coolant，才RM 18


Plug suitable for persona:

NGK TR6 IX
Denso IT 20
Bosch HGR7QDI