My 2002 4.0liter looses coolant over time. I am not sure where it is going. About ever 3000 miles or so I have to add coolant to the overflow tank, from the add line to full line. So maybe a 1/4 gallonish. My oil is clean. I see no drips of wet areas in the engine compartment. I never smell the sweet odor of Anti-Freeze. Just kinda wondering if this could be warning that something is going to fail in the future. Thanks

 

Get a cooling system pressure tester at the auto parts store. Wait until the engine is cooled down, and there is no pressure present, and attach it in place of the radiator cap. Pump it up to the systems operating pressure on the cap. Watch the gauge to see that it's in fact losing pressure. No pressure loss means no leak, maybe the overflow has a hole in it...
It will show any external leaks in the system. A pressure leak from a crack in the port area of the head could probably be heard through the throttle body with a mechanics stethoscope.