*TS - sir I bet, pure tap/distilled water lang ang gamit niyo? tama po ba?

you said kung normal city driving lang, no overheat. kung long drive overheating ka. tandaan na ang water maganda ang cooling power pero mabilis maabot ang boiling point, hence in long drive umaabot na ng boiling point ang water.

my recommendation, put 50-50 coolant in your radiator. in your reservoir naman, pure coolant. unahin mo muna itong gawin sir, yung ibang recommendations na nabasa ko dito masyado kaagad malala, always start from the basics.