The crank case breather hoses are part of the engines system designed to keep harmful emissions from getting out into the environment. The hose recirculation fumes and gases from within the engine block back into the combustion chamber to be burnt clean. There are three breather hoses on the Mercedes C320 and if you are performing any work on the injectors, MAF or valve gaskets that involve moving the hoses you can pretty much count on replacing them. The hoses sit on top of the valve covers and get extremely hard and brittle with age. There is one hose on the right side and two hoses on the left. While the right side hose traditionally last longer than the other two, if you are going to be working around the heads plan on replacing all three.
You will need to remove the air filters to complete this job. Please see our article on replacing your air filters.
Installation is the reverse of removal.
The right side hose connects to the top of the right side valve cover (red arrow). If it is still pliable slide it off where it connects. If it is not, it is easier to just cut it off as you are going to be replacing it anyway.
There are two hoses connected on the left side (red arrows). If they are still pliable slide them off where they connect and then go celebrate as you are the first person I have ever heard of to successfully remove them without damaging them. If they are not, it is easier to just cut them off as you are going to be replacing them anyway.
The larger hose on the left side connects down onto the lower part of the MAF housing (red arrow). It is very difficult to reach. If you have small hands you may be able to remove the old hose and attach the new on with the housing in place, but I find it easier to remove the MAF housing. It is easy, quick to do and we have an article on it to walk you through it.
The smaller hose on the left side is two pieces (red arrow), and can usually be separated by the MAF connection for easier replacement. The yellow arrow shows the area you need to work in if you are leaving the MAF housing on when replacing the larger hose.