I have just recently put a new koyorad radiator in and a week later a rock hit one of the veins and it started leaking i patched it up with some jb weld and everything was fine for about 4 days. now the motor is starting to over heat again so i have parked the s2k while i wait for a new radiator. My question is why did it run fine for 4-5 days and now it is over heating? I thought maybe my thermostat was going out but it is pushing fluid in and out of the motor. While the car sits running it does not over heat but the second i start driving it over heats. Im starting with the radiator, but it seems like rolling it would cool better because the radiator is getting air into it... so what could my problem be?

 

It probably was leaking past the JB weld at temperature, or you lost enough fluid during that and needed to bleed it better. When there is air in the system there are all sorts of odd behaviors that can happen.

When you're running at higher RPMs the engine makes more heat. That may be why it's fine at idle.

I would change the thermostat out if it's got more than 8 yrs or 80k mi on it. It's good PM.

 

Yeah i bleed the system by opening the valve by the fire wall and also the one by the intake, and filled till coolant started coming out. The car is a 05 with less then 50K on it. It might have been still leaking but i don't understand why it would run hot and when i check the radiator it is still topped off.

 

^RAdiator might not be holding pressure - lowe rpressure = lower boiling point, once it starts film boiling, heat transfer drops = high temp spike?

 

That, and it may require a lot more than just letting the two ports run clear for a few seconds. When I did the last bleed on an S2 I had to run the two ports into a catch container, then run the car at temp for about 20 minutes while the nose was lifted in the air to get all the air out and get heat back.