I'm not a Corvette guy, but I am helping a friend with an '08 C6 Convertible. He asked for help saying that he had driven his Vette to work and saw a big puddle of coolant under it after work. (He filled it up with coolant and drove it home.) I did a quick inspection and his engine bay was a bit of a mess. There was some fluid residue on the power steering rack,(underneath the front top coolant hose) but he admitted that he has never cleaned out the engine bay and that it might be an old leak. I checked the coolant level and it was full, so I asked him to drive it a couple of miles to warm it up enough for the thermostat to open up so I could see if anything was currently leaking. He decided to drive way farther than a mile or two and was probably hot-rodding it. When he came back 30 minutes later, the engine was smoking and the temp gauge read nearly 245F! (No, I did NOT advise him to do this. It hurt me to watch him abuse his car like that, just like it probably hurts you guys to hear about it.)

Observations:

1. Both of the straps that hold the air filter on were loose and there was plenty of air leaking in from that area (I don't know where the airflow sensor is on Corvettes, so I don't know if this air leak might have caused a lean mixture to contribute to the overheating
2. The coolant reservoir was still full and there was no obvious leaking.
3. The radiator fans were not running. Neither of the 30A cooling fan fuses looked bad, but I didn't have any electrical test gear with me. I saw the car has 3 cooling fan relays, so I am assuming that if only one was bad, the other fan would probably still work)
4. The smoke wasn't thick and I couldn't localize it except it looked like it was coming from the area of the engine block and heads. (Possibly burning off old dirt/grime that survived normal driving but smoked at the higher engine temps). It had no particular smell beyond a light burnt smell. (Didn't smell like burning oil or coolant)

My guess is that #3 might be the issue and #1 might be part of it if an airbox leak would throw off the airflow sensor. Does this sound reasonable?
When I go back with electrical test equipment, I'll confirm the relays work, and that the fuses are OK. Beyond that, I can confirm that the fans are/aren't getting power, which leads to two questions:
1) Are the fans simple on/off fans or do they run off of a PWM signal? (IOW, if I find +12v going to the fan and it isn't turning, does that mean the fan is dead, or that it isn't getting a PWM signal to turn)
2) Does the C6 have any common issues with fans not working I should know about? Is there any part of the system that I should focus on?

And finally, can anyone think of a reason why his vehicle would've leaked while parked previously, but showed no sign of leaking when the coolant was ridiculously hot? My original theory was a leak in the upper coolant hose that should have begun leaking as soon as the thermostat opened up, but there was no evidence of a leak there, so that theory is blown.

 

The AFM is downstream of the airboxes. It's immediately before the accordion-shaped hose in the center of the engine. I don't think this is your problem.
The fans are variable-speed PWM.
Yes. The fan connector can burn up. It's the three-terminal plug that goes in the silver box on the right side of the cooling fan. Inspect it closely. This is usually the problem.
The leak could have come from the pressure relief on the surge tank. Now there's less coolant in it, and/or it's not as hot. The system can go over 245°F without burping coolant.

 

I will be checking this out. Does it burn up on the fan side (requiring the fan to be replaced) or on the wiring side (requiring a new pigtail)?
This is actually a big relief. I don't know the specifics of Corvettes, but I know many aluminum block/aluminum head engines don't handle overheating well. I wasn't looking forward to explaining to him that his heads or block had warped. Knowing that 245F is inside the realm of survivable is a load off my mind. How hot can these things run with reasonable safety?

 

Might want to check the seals on the plastic rad tanks. Mine would only leak after cool down. Good luck!

 

The seals under the screw-off lid? Somewhere else? The lid did seem relatively loose, but I didn't think the plastic tanks were pressurized.

 

On the wiring side. The connector housing and terminals are available. Do a search for "fan connector".
The COOLANT OVER TEMPERATURE message doesn't come on until 255°F.
All cooling systems are pressurized by heat expansion. The Corvette's stock relief valve opens at 18psi. That said, LightningBrett is referring to the plastic end tanks that make up the radiator itself. They can leak where they join up to the aluminum core.