Kia Sorento Overheating

I own a Kia Sorento and I still consider the car to be good value for money. I am currently on 60 000 km an my motor plan covers me till 100 000 km. Recently my car has started over heating I took it twice to Kia Midrand, once to Kia Centurion and lastly to Kia Gold Reef City twice but my car is still over heating. If I take the car to a mechanic outside of the dealerships I will lose my motor plan. If my engine eventually ceases Motor plan will not cover me as it will be as if I purposefully rode the car to death. I need help because it doesn't look like there is a dealership which can fix my problem.