yep although I didn't pull the thermostat put and flush the entire water line, I took the radiator out instead and flush it, a lot of blackish shit water with some piece of little rusty metal came out, after flushing the radiator like this for 5 mins and put it back to the car I used a bottle of "radiator flush" addictive and run the car for an hour, drained it and put fresh water in and drained it and put coolant in, and it becomes a lot better now. I guess most of the dirt deposite at the bottom and the core of the radiator.