I topped off the coolant about 3 weeks ago to the max line and now it's gone down a good amount, maybe 4 inches below the max line. The car is not leaking coolant... any ideas where it's going?

Well, obviously it's leaking somewhere - I suppose you just aren't actually seeing a drip anywhere.

You're best case is that the radiator cap is not holding pressure. Check that first.

Next, you can have a shop perform a classic pressure test to see if the overall cooling system holds pressure. If it doesn't, then the detective work begins: ck hoses, clamps, gaskets. Worst case is an engine block leak, and I think there are ways to check your oil for coolant contamination.

A little can burn over time but not that much over such a short time.

Well the car is under warranty so I will be taking it to the dealer soon.

i had that problem too. Don't worry it's not leaking. At any given point there will be a differernt amount of fluid actually in the radiator depending when you turned off your car.

+1... check it each time after car cools down completely.

I checked it today after driving it for a bit and it's back to the max line? Is it just thermal expansion?

You may have topped it off when it was hot and checked it the first time after it had cooled.

Are you supposed to add coolant through the overflow bottle or through the radiator cap?

If you are just topping it off add in the reservoir… as long as the reservoir was not bone dry… if it is/was you have lost too much coolant.

No I topped it off when the engine was cold.