I had the same problem two weeks ago, the crack was on the top but you wouldn't see it until you remove the radiator. I bought a replacement one off Ebay for $56 with lifetime warranty and it fit perfectly and has been working fine ever since...

 

So about a week ago I was at a dealership, looking at getting into another car. While standing there(looking at a nasty zl1 1le) I heard my belts squealing and saw that my radiator was smoking bad. I ran over to tell my gf to turn it off, more like " turn it off,turn it off, TURN IT OFF! as I'm running over, I see coolant spewing out of the bottom. We're stuck. I don't want to start it, even though I know I can, who would want to risk the damage. Anyway, my grandfather saves us at 3 am by bringing us his car, we take the g to my work, thankfully literally a block away. My grandpa lives about 5 mins from that area, so we pretty much had it made in that sense. I leave it over night, the next day I get it to his house. The first time I tried to move it the night it did that, I had to stop 3 times. Like I said, literally about a 1/2 mile. When I drive it to his house, I filled it with water and it was like nothing happened. After starting it and letting it run for about 15 mins, it was a very slow drip. I checked all hoses, all seals, all connections etc etc. Everything was fine. So a few days later we go to take it out. It was actually pretty fun. It wasn't something anybody could do, but if you have some experience, replace your radiator and you will feel very accomplished lol. Anyway, new radiator comes in tomorrow, so the update will follow! Hopefully you got your radiator situation taken care of and you were able to do it yourself!

 

99% of the time its the radiator unfortunately. I thought the same with mine but of course turned out the radiator was bad.