I have a 1989 Honda Accord that was overheating when going up high grade hills only and on long freeway trips, I was told the radiator is rotted out so I replaced it with a new one as well as two older hoses and I bled the air valve. Everything seemed better for a couple of days, and then I went down the mountain as I live at 5,000 feet and drove around town for a while on flat land and it was fine, as soon as I began to go back up the mountain the car began to over heat again, I stopped and it cooled down quickly, but it continues to overheat only when going up hill and on very long freeway trips. There is no white smoke coming out of the muffler Oil is clean, no froth, or milkiness Coolant is clean and bright green, Car runs great, as always with power and drive. I am not losing coolant regularly, but when it overheats I can see coolant sputtering from the top of the overflow tank, and then it stops, and once the car is cool, the overflow tank is fine and full of coolant. Today the car started to get hot on the uphill again and I pulled over and when I opened the hood there was coolant sputtering out of the radiator cap for the first time throughout all this, I waited a little while and made sure the cap was tight and went home. The car stayed cool because I was on flat ground and when I got home the radiator cap seemed fine, the cap is a few months old and was the one I used with the old radiator. 1. I did not change the thermostat when I changed the radiator--should I have? 2. I did not buy a new cap for the new radiator, used the old one which was only a few months old, should I get a new one? 3. Also, the cooling system air bleeder valve, can it be stripped and releasing pressure? as I noticed today there was a drop of coolant on it after overheating and it should be sealed tight???? Help please, I do not know what to check and do next???? Thanks for your time.