Coolant Expansion Tank purpose of cap hose
 

What is the purpose of the upper hose on the coolant expansion tank that goes from the cap to in between the passenger front fenders? On a 124 1995 E 320.

Mine is broken need to replace but is very hard to reach the cavity that goes into, is it just for venting?

Yes it is for venting the fluid if the pressure gets too high and the cap releases some coolant....

There is actually an overflow tank in there if you take the fender off. I am replacing my tank if I have time I will take the fender off and post some pictures, and no you dont have to remove the front bumper to get the fender off. Just the fender skirt piece and one bolt on the bumper mount.

Thanks for the help and advice

It turn out that besides a broken hose the rubber seal on the expansion tank cap have fallen apart and it was causing all kinds of problems (overheating and losing of coolant) I will replace both

Here is a very informative link on the function of the expansion tank

http://www.custompistols.com/cars/articles/overflow.htm

Best regards