Take your radiator cap off when the car is cold then start it. If it keeps bleeding off air bubbles then the compression of the cylinder is more pressure than the coolant system so thats why you don't see it with the engine running but when you turn it off the compression in the cylinder is no longer there and the pressure of the cooling system is able to pump the coolant into the cylinder while it sits. Ask me how I know Also after you turn off the engine listen to it. See if its making any weird and unusual noises. Mine was making kinda of gurgling noise but it was very subtle until I was under the car looking at stuff then I could hear it.

 

Bad96firechicken!

If your car is running rich and you have catalyst converters it will smell like sulfur. It will also produce white steamy smoke! All cars will steam a little at startup no matter if weather is cold or hot. Mine does it!

As long as you don't loose coolant your okay as far as your engine having a head gasket leak.

I really think all the problem you are having is just a rich running condition Fixit!