After replacing my radiator, waterpump, top and bottom hose and thermostat. I have got a very small amount of brown on my radiator cap, am getting over heating (at idle) loses a little coolant and has power loss. Can't get compression test done yet due to fundage.
Check the overflow for oily bubbly looking things. Warm up the engine, carefully take off the rad cap and look for air bubbles. Check for steam out the exhaust only when engine is warmed up properly.
Intake manifold gaskets are more common to go than head gaskets. If there's no water in the oil the head gasket might be ok. You say it's overheating on idle, are you 100% sure it was bled properly after doing all that cooling system work?
Inlet Manifold gaskets would be the go if you have brown sludge......if it was milky then head gaskets would be where I would be looking. Inlet manifold gaskets are probably the most common thing to go on the ecotec's as they are made out of a plastic prone to cracking.....if you short on money its not something you have to replace straight away but keep an eye on the colour of the oil, if it looks like coolant is getting into the oil stop driving it until you can get it fixed. As for the overheating make sure the system has been bled correctly.
