How to Add Coolant: Mercury Grand Marquis (1992-2011 Click to view0:19Adding engine coolant (also known as antifreeze) to your 1999 Mercury Grand Marquis is pretty easy. Engine coolant circulates through your engine to keep it cool in the summer but won't freeze in the winter. Make sure to check your engine Author: David Hobbs Engine Cooling System Problems of Mercury Grand Marquis Mercury Grand Marquis owners have reported 39 problems related to engine cooling system (under the engine and engine cooling category). The most recently reported issues are listed below. Also please check out the statistics and reliability analysis of Mercury Grand Marquis based on all problems reported for the Grand Marquis.