88 grand marquis overheating and leaking water

Sounds like the heater core is bad.

Yes I agree, and running low on coolant.

I appreciate the help. But out of curiosity how did you come up with that answer?

The location of the leak. But we should ask do you smell anti freeze inside the vehicle?

Also check heater core hoses, they old enough to be bad.

The heater core is located under the dash on the passengers side so if it starts to leak anti freeze will go onto passenger side floor.

And that is a good question from Rowefast do you smell anti freeze or is it just plain water that you see on passenger side floor ?

No antifreeze in the car period just water. I don't put antifreeze in the car

You should run a 50/50 mix. It raises the boiling point of the coolant and cools the motor much better. Just check your heater hoses running to the heater core, replace the heater core if necessary.

Plus the anti freeze is a rust prohibitor.