RIght so heres the breakdown...
420a, new aluminum radiator.... good hoses, it does have liquid in it...
This guy was overheating on RUSH hour, got in the freeway it cooled down... i still stopped at a gas station trying to refill the damned thing (turned out it did have water) and apparently issues was solved.

TOOOday... i had a low tire... so i filled it up... i got into the car and it was hot again... i was like wtf?! i drove home and it was fine on the way home... i stopped on the driveway.. let it idle... started overheating... revved and the temp went low... let it idle again and it rose one more time....
Am i havin a problem with the water pump? the thermostat?! why is my heat going nuts?!

 

Is your fan coming on?

 

change your thermostat. my old RS did the same thing and i couldnt figure it out untill my friend said to check it.

 

yeah the fan comes on... well 1 of them... my guess is that the other one is for the a/c right? and how about a 180 failsafe thermostat? i think it has never been changed by the previous owners

 

I still think its your waterpump. I have a 420A been in the same case as you sitting in traffic with A/C on. A/C went warm temp rose. On the highway temp fine, at a stand still temp high

 

No a/c... in my car there's only a/c if its hot outside and theres a girl in the car... and about the water pump... well could be a possibility but when i was idling the car withouth the radiator cap a while ago i could see the water circulating... so... i think im gonna go with the thermostat for the moment.... any possibility that my new radiator could be toooo small? or something like that?

EDIT: how much of a common issue is this on a 420a?

 

no, guaranteed its your thermostat. mine did the exact same thing. when you drive it cools down, or rev it when its stopped. but when your at idle the temp sky rockets. if it was your pump, it would just over heat, moving or standing still.

those thing got kind of a fail safe when it breaks, your car can still cool down when you drive,so its like a warning when it happens so it just doesnt cause major damage. trust me i come from a family of Master Tech's

 

lol.. thnx for the info then... im still gonna change the thermostat cuz i dont really want to see the freaking nieedle going ALL the way to the top.... it gets me soo stressed out... but yeah.... when you drive it cools... you rev it cools... but idle... man feels like im gonna blow the engine!!

 

i have the same problem with my rs and i have no clue what it is

 

try changing your therostat first and go from there.