Engine stalling while on the road

My car is a suzuki aerio year 2002. At first the car used to move for about 20kms and stalls on the road. After resting for about 10 mins, the engine starts and does another 5 kms and stall again. I later realized the problem is over heating. I am in kenya which s a tropical country and my mechanic removed a thermostat from the coolant loop and catalytic converter in the exhaust manifold and changed the temperature switch. The car improved a bit but the problem is still persistent. The car has bad hard-start. This did not improve and I have to run the fans continuous. When fans are running continuous, the car looses power especially when climbing hills. What could be the problem? What is the remedy? Have you experienced this problem before?