My pontiac is losing about half a gallon of Coolant per week. Also...
I don't know if it's unrelated or not but the AC sometimes stops blowing cold on driver's
I drive this car to and from work (44 miles a day) six days a week. The floor under the
car, AT my place of residence, is not stained. There is no "mayo" on the oil filler cap
and the oil on the dipstick looks normal.
I have used this before and it worked for me but no promises to you but if I were you i would give it a try. Its called Bars Radiator and Cooling System Stop leak. Now a few people will say not to use it because it will clogg up your cooling system and it would if you use more then that is recommended so if you do decide to try it and it does not work the first time do not keep adding more hoping it will work that is when you will clogg up your cooling system. Its been working in my cooling system for almost two years now and no problems. The A.C problem is unrelated that is another problem.
You can do what friebird suggests or find the leak, could be ahose, radiator, water pump, etc. and repair to stop the car from losing coolant. The AC is a blend door issue or your low on refridgerant. Might be time for a trip to the local garage.
Agree its good to find the leak if you can. Check the plastic elbows from engine to heater. They like to blow up and leave you stranded. If you can't find it though Bars Leak is an excellent product. You can actually use two applications if one doesn't work, but no more than that. I "fixed" my GP with it several years ago and add a couple of quarts of coolant a year and that's it. No guarantees of course, but it makes more sense than spending hundreds on an old car.
Check the heater core. They do not always leak into the car
Looking for a Used Grand Prix in your area?
CarGurus has 2,846 nationwide Grand Prix listings starting at $1,995.
Search Pontiac Grand Prix Questions
Pontiac Grand Prix Experts