Mention your city. 10w40 ya 5w40 use karein. 20w50 se apka heat up ke issues mazeed kharaab hosakte hain. Change gasket, make sure cooling system is all working. Thermostat in place, auto fan, no rust in cooling system and heater attached. Havoline coolant with 50/50 premix with battery water and you'll problems will be solved.