why is my car losing coolant?

Are you sure its not overheating because its of a coolant leak and getting low on coolant?

No. I don't see any water or coolant underneath. Could it possibly be the radiator? I add about one-half gallon of coolant every week lately.

I was asking you if your car was overheating because it was low on coolant from a leak?That would change the way you looked at it.We have to look for a leak causing the overheating?Or why its overheating causing it to loose coolant by building too much pressure and leaking coolant thru the cap?Are you sure its overheating before the coolant gets low?You could also have a radiator cap that is weak and not holding the correct pressure and loosing coolant that way.A bad cap is commonly over looked.

I bought a cap last week, thinking it was the cause, but it happened again. I don't see fluid on the ground after I stop the car. Could there be a leak, and if so, any possibilities?

There could be a leak anywhere radiator a hose loose clamp seal gasket this goes on.So is the car overheating i ask again?Iam not there if i was then i could answer my own questions.Like said before we need to know if your car is overheating and leaking over the cap or there is just a leak somewhere.There is no magic answer here iam sorry.First thing we need to do is find out if its overheating?

I checked again. I don't see a leak under the car, but I do see a spray or wet spot on the left side of the engine near the radiator overflow container. i am asking you...could there be a leak?

There could be a leak or it could be overheating and boiling over the radiator cap loosing coolant that way.I dont know if its loosing coolant or just overheating?Is it overheating?If not then you need to do a coolant pressure test on the cooling system.They rent coolant pressure testers at auto zone not sure if they will have the correct adapter for your car but you can check.