Radiator coolant

[EVO-V]

I'm still using the stock toyota long life coolant. During my last pms sa casa, I saw the mechanic topping off the reservoir with tap water from half level, tanong ko lang sir kung kelangan na palitan yung coolant kasi compromised na sya.

Those coolants are water soluble. May tolerate a bit of dilution especially if the water component has evaporated.

The quality of the water is more critical when topping off. But tap generally should be fine.