Hello! On January aper some strange liquid on the coolante... The mechanica said its cause buy the new water pump. But now it's back again.
It'a the head gasket?

 

That definitely is one possibility and what I thought was very likely your problem way back when you first posted this. Things like a cracked block could also do this but that is pretty rare (so is a head gasket on a 4 cylinder C Class).

 

well if the head gasket is in good condition what cause this color?

 

do a $90 car inspection.

 

prepare to spend $1200-2000

 

Ya my car had the same thing and it turned out to be the head gasket. cost me 1500 dollars.