Coolant System Leak, it's not a hose!
 

On my 400E the coolant is leaking out at a fairly fast rate, about 1 to 2 days. This morning I jacked the car up to find where the leak is. After pouring several liters of water in the system it soon started to leak, so then I got under the car and pinpointed the leak. It is leaking out of a small black plastic box located under the crankshaft pulley. There is a 1/2" diameter hose that connects it to the water pump. The box itself though has several slits in it to let the water out. Puzzled I popped in my MB service manual CD and found a PDF file that had some information on it. It said that the hose and tank are the coolant drain line and reservoir. I does not make sense to me, I figure that there must be some valve either in the reservoir or just before the small hose that might be ruined. If anyone knows of a possible cause please HELP!

Leaking coolant
 

Replace the Waterpump,the black box is just a catch tank

Thanks for the info, I went to the mechanic to be sure and he said that the box is a catch tank and is there to make sure the owner can see the water drip on the ground so it doesn't burn on the engine block.