Heater won't get hot. Thermostat is ok diverter door works. What else do I check
Check the heater control valve.
And you may have air in the system that needs to bled out, or a plugged heater core. Make sure the engine gets to operating temp. of 195 to around 200* to insure a good thermostat.
be sure your coolant in the rad and expansion bottle is topped up
Looking for a Used Grand Marquis in your area?
CarGurus has 8 nationwide Grand Marquis listings and the tools to find you a great deal.
Search Mercury Grand Marquis Questions
Mercury Grand Marquis Experts