2004 Grand Prix "Lost Compression"

There's a couple of things that could be going on. Pouring cold water into a hot engine when it's not running is not good! With the radiator full of cold water it will rush into the hot engine when you start it up. Pouring cold water slowly into the hot engine while it's running is the thing to do, like you said. He might have cracked the block or a head! But it most likely would still run. It wouldn't run well, but it would still run. My suspicion is the coil packs are fried or the ignition control module is fried or both from the excess heat. Check for spark. Spray a little starting fluid down the throttle body. It should run a few seconds on that. If not confirm you have no spark. I bet you don't and that's why it won't run. Hope that helps! Jim

And... my favoritest answer of all. Scan it for trouble codes. That may give you some guidance.