we have a 2002 vette that will push water out of the cooling system ...
have improved the problem,it first came in and while idling 5-10 minutes would push water out of the system,
the engine was pulled for oil leaks, at that time the heads were worked and checked out, new GM head bolts and gaskets were replaced,
also had a lot of aftermarket parts on it , so the water pump, thermostat, and surge tank also replaced (all GM)...
we confirmed the fans work as designed, also has new radiator.
now when it is driven , as soon as you stop it will push water out .
we pressure tested it over night and it passed...
also preformed the CO2 test and it passed ....
have never seen anything thing this weird....
thank you scott

 

I'm going to guess you have air trapped in the system.

 

Surge line and steam line swapped on the radiator?

 

What do you mean by push water? The overflow tank is leaking (spraying) water?? I'm assuming it's overheating?

 

The system needs to be burped of air. I usually put my front end in the air and leave the cap off to do this but others have different methods. Check this thread and see if it resolves your issue: C5 Coolant Bleed

 

+1 bleed air out from stream crossover tube.