The only reason for Mehran to heat up excessively is keeping the car still under scorching sun with 4 passengers. When ever you get stuck in traffic ( Most common issue for karachi people ), turn off AC . But if you keep your car running at a speed of 25 kilometre / hour or more, then you will not face this issue. Type of coolant is unlikely to yield significant cooling performance. ( Although Nasa coolant is fairly good enough, recommended by PakSuzuki and costs 200 rupees/litre)
Do these things
1 - Keep your radiator clean . This is probably the most important factor.
2 - Your fan should be working properly.
Also note that 50% engine heat is NORMAL for mehran. More than 60% implies over heating. More than 70% means you should definitely stop your car and wait a while for it to cool down.