I agree with the others. If you can smell coolant, then you probably have a leak somewhere. The red buoy floats on the coolant, so it should not go down when you shake it. I am thinking that it could be going down when you shake it becasue the coolant level is low and the buoy is sticking.

My initial thoughts are water pump or valley pan gaskets, which are unfortunately expensive reapirs. I had those items replaced on my 02 4.4 under warranty at about 80k miles. I would suspect that if you had a top side leak such as a hose or expansion tank, that you would see a white residue from dried coolant on the affected areas and the hood insulation. I know I did when my expansion was leaking.

You should not have to add coolant at all after the system is topped off and all the air bubbles are worked out, so you may need to get your system pressure tested to find the issue.

Good luck