Dear All:
All of a sudden, I got a coolant leak. Ironically, it does not leak when the car is running; but, as soon as I shut the car off, it starts leaking with a steady stream. I cannot figure out where it is coming from, at least when I look from both top and bottom , I cannot see the location of the leak. The coolant runs along the plastic channel piece that is below the radiator.

Any hint would be much appreciated.
Regards,

I googled E320 overflow tank and got this. Could one of the small hoses under the tank come off? Worth a look.

http://www.carparts.com/details/Merc...E&gclsrc=aw.ds

I have already checked that - no issue. The coolant seems to come on the lower levels (I think). Moreover, why should it start leaking form the reservoir, after I shut off the engine?!
Thanks very much for your comment, anyway.
Cheers,

How stiff is your radiator hose after the car has been allowed to cool overnight? If there's still pressure in it, you might want to do a pressure test on the cooling system to see if you've got a blown head gasket. Other than that, I wonder if you've got a water pump going bad.

Very good points. A pressure test would simulate the expansion of the coolant after the car shuts off.

As I stated above, it leaks with a steady stream after I shut off the engine. Therefore, there is no pressure left inside the circuit!
Cheers

Understood. I think rapidoxidation has the right place to start. A pressure test.

Yes, that I what I am going to do tonight hopefully.
Thanks again!

If that's the case, then a pressure test on the cooling system will allow you to see where the coolant is being pushed from. Take the bottom plastic panels off, pressurize the system, and start looking closely.

That is the plan!
Cheers,

Faridtaheri, Coolant systems still have pressure after you shut off the motor if the motor is in normal operating temperatures because the coolant expands when hot. Make sure you do not overfill the overflow reservoir/expansion tank when it is hot. You are almost guaranteed to have it leak out the excess. When you shut of the motor, the engine actually gets a little hotter because the coolant is no longer flowing and not cooling down and it builds up pressure.

Coolant pump would be my first suspect.
With pump turning the centrifugal force keeps coolant out of shaft seal, but when the engine stops, it will pour via bad seal.
Bottom of the pump housing has small drainage hole. Try to get to it, or stick your phone camera to confirm.
Leak will have washed out dirt in the area.

OK! I will definitely check the coolant pump (same as water pump I hope?!).
However, I had a leak on my Beemer's water pump, but, that was leaking all the time, not when only engine gets shut off! In any case, I will investigate the pump.
Cheers,
Farid

It is the same thing, but depends how you use it.
That reminds me the old joke that the same brush can be:
-toothbrush
-fingernail brush
-shoe cleaning brush.
But don't you dare to reverse the order.