While draining and refilling the coolant on my 560sl, I heard a clanging noise upon startup that was clearly coming from the water pump. Pump was replaced 3 years ago so pump shouldn't be worn. Figured that the pump was running dry and was not priming. Shut it down and tried a few things that didn't work and then referred to manual. Manual indicated that heater must be on and that the recirculating water pump must also be on. Did that but pump still clanged indicating running dry. I then remembered that manual indicated revving the engine to prime. Revving did the trick, but did I damage the pump? Hope not since replacing is a *****!!!!!!!