ok, i replaced my radiator today. when i started it up the idle started jumping from like 1k-1700. i figured there was just air in the system but i left the cap off and let it run. finally, i was like ---- it. maybe if i drive it, it will cycle. after driving about 1/4 slowly it still kept doing it. so when i turned around to go back to my house in 1st thru 3rd i took it to like 5500 then stopped. and the idle also calmed down. but i noticed there was steam coming from under my hood, it was coming from that bleeder valve looking thing on the upper radiator hose. i turned the car off and closed that tight. it stopped. on the way to my friends house about three miles down the road my temp guage was right at the hot line so i through it in neutral and coasted and after a lil bit of coasting it went down to almost normal. but then when i start driving again it starts climbing up again. anyone know my problem?? p.s. my fan is working. o and the idle jumps slightly from like 800 to 1100.

 

i don't know about the idle, but if your temp is going up and down like you explain, then you have air in your coolant system. you need to bleed it properly, not leave the cap off, that doesn't bleed it. use the bleed screw as you mentioned. then top it up. your temp starts to rise turn your heater on full blast to bring it back down. if it does not affect the temp at all then you definitely have air in your system.

 

or your headgasket it tizoast

 

how do i use the bleeder valve? with car on or off?

 

on, you open it to bleed the air out of the system.