quick question, what is this ? it's leaking coolant
 

so lots of coolant leaks out of the engine right after i shut it off lately, i tried to trace it and there's lots of it right behind that pulley in the picture, any one knows whats that ? :confused:



http://img23.imageshack.us/img23/6660/engd4copy.jpg

If your loosing coolant behind the pulley wheel and that is where your waterpump is then im afraid you waterpump is worn out.

I recently changed one on my wifes C class and was quite easy, but for the CLK its a little more cramped in the engine bay but still do-able. If you can use a mirror and look behind the pulley wheel at the waterpump, you will probably find the water is coming out of a small tube about 10mm in diameter. This is a pre-warning tube that will start to release water when the pump is on its way out. (see photo)
If its stated leaking then you will find that you will need to top the coolant up more and more each day as the seal wears.

Good Luck

Thanks so much for the detailed answer, I thought that the water pump is behind the fan clutch for some reason, I'll take her apart tomorrow and try to change it.

i've been searching everywhere to see how to change the water pump and all the instruction says the water pump is behind the fan clutch, not that pulley :S :nix: are you sure the water pump is behind that pulley with the arrow ? Thanks

YES IT IS

Speaking of coolant: Where is the drain plug for the coolant system?

Having recently replaced my water pump I assure you with proper tools it can be done in a day no problem. The pulley you illustrated is the belt tension arm however. This doesn't exclude the water pump as the source. When mine went she threw coolant all over the engine bay. Your original suspicion is correct however in that the water pump is indeed behind the fan clutch.

Passenger side of the block, by the motor mount. After the radiator is drained, only a few drops come from the block drain plug. Mine is never coming out again.

my pump just went too, is it the whole assembly? when i looked it up on some sites, they have ones with/without oil cooler intake.

some diagram show a big piece block shape and others look small spout or is that just a generic pic they use.