Coolant is evaporating, & there's no leaks - Cars & Trucks

If you are losing coolant in a modern automobile at any significant rate of loss, then there most certainly IS a leak. The most common source of undetected leakage is from a worn out water pump. Many newer cars have their water pump concealed in the area of the timing belt. Here the coolant leaks out and evaporates on the engine block before there is any ability to visually detect it. Even older cars that have external pumps have "weep holes" under the drive pulley to provide early detection of impeding failure. Often, however, these leaks also evaporate on the engine before detection as many of these pumps are hidden well behind and under other components. Water pumps also have the "magic" ability to not leak when the engine stops rotating, even while there is still pressure in the cooling system, so you rarely get any coolant puddling under the vehicle to give away the problem. If the vehicle has more than 70K miles and has never had the water pump replaced, that is probably the first thing I would check out.