After rereading my previous reply, I have to clarify that you can add a bottle of dark purple dye to the cooling system, THEN drive it a while, then check for bright yellow stains with a black light.
A water pump does normally leak all the time, but it is also common for some to not leak when the engine is warm. It depends on how it fails. If the rubber lip seal wears out, it can expand and seal when warm or when the normal pressure buildup pushes the seal against the spinning shaft. Seal failure is most common when running just water in the system. Antifreeze contains seal conditioners, water pump lubricant, and corrosion preventers.
If the bearings wear out they will let the water pump's shaft wobble and move away from the lip seal. The drive belt holds the shaft off-center so it will leak all the time. Nothing will solve that except replacement of the pump.
Monday, April 11th, 2011 AT 5:31 PM