If the temp drops down to normal when the vehicle is moving, then it is an airflow problem. The fan's age has no bearing on its functional ability.How well does the shroud fit the radiator and fan combo? Don't think that more coolant in the ratio will help either. Water cools better than
antifreeze. Is the water pump the correct rotation? They come in standard ratation(clockwise) and reverse rotation for serpentine setups.