With a cold engine, there is coolant up to the top of the radiator, and the overflow tank is above the max line.

Also, kinda random, but yesterday after driving around for a while, the driver's side fender was really hot. The hood was not. When I popped the hood, I noticed that on the driver's side, the Carbing carbon fiber radiator cooling plate looks like it has started to warp around the radiator stay, as if there was excessive heat. Am I crazy, or does this mean something?

 

Bump for help!

 

Bump for help, starting to happen again!

 

Yeah this makes no sense as the heater usually makes your car cool down by opening up the coolant path.

 

Yeah, I drove around with it on full cool all summer and it was totally fine. We just got a cold front after the tropical storm passed through, so I turned the heat on again -- bam, overheating. Makes no sense, unless there is something that opens up when you turn the heat on, and that is somehow letting air in the system?

 

is your heater super hot like it should be or is it slightly warm?? If you have a coolant leak someplace the heater not being super hot is one way to tell it has air in the heater core which will mke the car run hot(air in the system)

I recently changed the radiator in mine and that heater core is a bitch to get all the air out. The only way to be sure the air is all out is by how hot the heater gets.. my 1st time bleeding the cooling system took 2 hours in a freinds S.

 

report back what you see. with the engine cold, start the car and take off the radiator cap. let it warm up and check if there is coolant flowing across that opening. you will lose coolant with this process. No flow = stuck thermo. I'm leaning this way since you said one side of the radiator was hot and the other side was cold. I'd suspect a blockage or bad thermo.

 

Bingo...check your heat temp...good call.

 

Yeah I'm sorry, I thought I had said that already. No heat is coming out when I turn on the heat, it goes to lukewarm and that's it (and today it was strictly cold still). So I bled the system and got the heat to come back, but fans weren't cycling and air was still coming out. As long as the heat is turned on, it continusously lets air into the system. Is there a way to test the heater core for leaks?

 

So let's say the heater core is leaking.
You're driving around with the heat off = route to heater core blocked = sealed system.
You turn the heat on = open the valve to the heater core = open the way to the leak.
Do you smell coolant in the interior?
Because there is pressure in the system, build-up while the valve to the heater core was closed.
This only works IF that valve can take the pressure.
If it can't you always have a leak in the system and you will never feel pressure in the hoses when hot + heater off.
Do you?
Its the same as starting the engine without the radiator cap (allthough that's a pretty big leak)
You'll get temperature but no pressure in the system.

I think a small leak - anywhere - always lets coolant out and never will let air in.

And what about the 20 seconds?
Still the same?

Did you use an OBDII to scan the ECT?