BMW power steering reservoir for splitting the I/C
It fits nicely to the passenger side front of the engine.
I ordered the parts to do this and never bothered as it doesn't do much. The systems are not shared. There is a single connection from the high point of the HE circuit to the cars cooling res and about the only way to get cross circulation between the two systems is to have active fluid loss in the HE circuit.
Splitting the systems makes a bigger difference on the C32 and SLK32 where the HE circuit is actively swapping a small amount of coolant with the engine cooling circuit to self bleed the system. This is not the case with the E55.
I could see doing a separate HE res if it has large and if the fluid in the res was put into active circulation to increase the capacity of the HE system (simply have a large res full of fluid won't do a thing if it is only a fill point for the system).
Just my $.02. If you still want to do it, I would sell my unused 335 res and bracket.



