I just had an issue with air trapped in my SDL coolant system.
After a few days the air worked its way to the top of the radiator, but I would follow the advice above and raise the front of the car slightly to help things along. You can tell if there is air in the rad if you squeeze the top hose and get very little resistance.
I then filled the coolant tank up to the point where coolant flowed to the rad through the 'vent tube'. This will displace any trapped air in the rad. It took about 2 Quarts to fill before the coolant backed-up through the vent tube. Since then, no problems.
