The hose which connects the reservoire to the radiator could be plugged. The radiator side tanks are know to crack , they are plastic. Look for traces of coolant on them.I have a couple concerns about both of my 89's coolant. The sedan has been having air bubbles in the colant once its driven long enough to fill the resevoir. It looks almost like boiling water. Should I start looking towards the intake gaskets?
Now while I was out replacing a few little things on the new coupe I opened the radiator cap and noticed the coolant level was low in the radiator but the overflow tank was pretty full. I think I'll be taking this one to work tommorow so I can check for the power steering leak so I'll keep an eye on that too. It was fine when I bought the car Saturday.