The aux pump normally runs for a while every time after I shut the engine off...

But today, after a short drive (<1 mile), I parked the truck and heard nothing! No hums. I thought the fuse might be out. Opened the hood, key in position 2, the pump runs. Removed the key, the pump stopped. Is there anything wrong here? 12k miles.

Gilly, is it possible that if the coolant temp is low enough (60c?) then the pump will not come on after shut down?

BTW, since the day one (sep. 2001), I noticed the coolant is 1/4 inch lower then the cold level line on the reservoir and it is getting lower and lower. Now it is 1/2 inch below the line, is this normal to ML? Added some water for now.