Grand marquis 1996 leaking coolant into the driver and pass side?
Leaking coolant into the cabin is always a sign of a failed heater core. You will need to remove the dashboard to access it for removal. A big job, sometimes left to the pros. If you want to tackle replacement, get a haynes manual or search online, youtube for instructions. Figure a couple days work, a shop will usually charge a full days labor.
Remove dashboard disconnect the a.c. harness then bypass heater core by purchasing elbow hose connecter cut the hoses from heater core at firewall connect two hoses coming from engine with elbow piece with clamps don't forget to clamp them just to by time
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