Thanks for all your help guys. My car was overheating when the ac was on or if I drove too much. The needle was also not steady. One guy here in the forum told me to check the crossover tubes coming from the heads because air can be trapped inside the engine. I checked that and they were stuffed really bad. I cleaned them with wire and blew compressed air and cleaned them. Now the car is maintaing temperature. I tested it by leaving the car with the AC on for one hour and it maintained temperature and ran really cool. Also the needle was steady. Thanks for your help, aprreciate it.