Overheating. water pump?
Also check your coolant/water mix.
You did use an LT1 thermostat (tall), right?
Not an SBC (short)
http://shbox.com/1/tstat.jpg
You can tell if the pump is running by opening the radiator cap (while it's cool).
You should see a steady stream of coolant pouring in just below the opening.
Don't do this when the coolant is hot, you will make a mess and could cause nasty burns.
Also, you didn't happen to remove your airdam, did you?
My air damn is still on.
Also, I talked to my brother. He said it could be the water pump about to go out, like not pumping a lot through the system, but enough to not cause it to get super hot, is this a possibility?


