My ECO maximum coolant level when cold will not stay there. A few times I have added a cup or more of Dex-Cool to the arrow on the side. I drive 40 miles, let it cool all day, & check. It falls an inch. The car gurgles about 10 minutes when I shut it off. There are no leaks on the ground or in the engine compartment. Outside the vehicle, there is a faint smell of coolant. The reservoir cap is snug tight. Does anyone know where my coolant is going & what the problem/correction is?