Car overheats when idling but cools down when running.

[tt335ci03cobra]

Could be intercooler pump not supplying properly, probably has air pockets. I doubt the motor is dead for the pump but the issue could be in the connection of the heat exchanger motor as well.

If the heat exchanger is not getting coolant flow, or has air pockets, your iat's will go through the roof until some airflow can cool that routed air.

One way to know if it's related to the intercooler or rather heat exchanger is to touch the heat exchanger after a drive, it should be coolish, touch the sc after a drive (mild to moderate not hoonigan drive) and it should be hot but not much over 130-140°.

If the heat exchanger is hot and the sc is boiling...

 

[mark23svt]

Mine did that, then eventually overheat to the point that I couldn't drive it. I changed fan and burped the system really well all good now.

 

[MIguel07]

Cool I'll check it out Saturday when I'm off of work.

 

[RED03SVT]

another thing to check is the relay connection. My brothers GT did the same thing and we couldn't figure out why. We replaced everything and the fan still wouldn't kick on. Come to find out the connection was loose.

 

[oster910]

So pretty much how the title states. The car overheats when it just sits there idling, but when I start driving it the temps drop down to normal. The temps do fluctuate when its running though. I see temps from 175 to 200 when running. what could it be?

my 4.75 stroker did the same, turned out the cams were the root cause, according to a motor builder not sure how that works

 

[Four Door SVT]

my 4.75 stroker did the same, turned out the cams were the root cause, according to a motor builder not sure how that works

Wait, what? Your cams? Find another lier to work with. So basically he said live with it or did he reinstall the cams with cool gel in them.

OP
Burp, the system check the fans and air flow across the radiator, especially check the condenser fins probably the most hidden culprit for your symptoms. Sometimes to burp properly it's messy so if you place a large funnel in the hole the taper can seal it while allowing fluid and air out and the fluid will go back in but the coolant can roll right past while the thermostat is open.

Make sure the funnel tip isn't long, protruding too deep in the purge hole can bottom out and not get a good seal and it needs to let air out so it should be just below the top.

Push the funnel in the hole turn it left and right, cut off below the mark the opening made on the funnel.

Run the car. Add coolant if it needs it so you can at least see it, coolant should flow past if not add coolant, when the thermostat opens flow should increase and air comes out or your topping off the coolant slowly to the top while its flowing past remove funnel insert plug.

A turkey baster can help remove overfilled coolant in the funnel while the car is running and prior to removing the funnel.