Still working on my 'up to speed heat'. I wanted to ask a specific question so I started a new thread. For back info look for my "weird heat problem thread'

I am getting heat at idle and around town. 60 mph plus, the heat turns luke warm at best.

I have pulled monovalve piston(brand new) out looking for a blockage. Under the piston, down low in the housing looks like a check ball(valve?) of some sort. Is it supposed to be there? could this be my blockage? It is not siezed up and looks to kind of float around down there....anyone??

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'89 300SE
'02 E320 Wagon

from what i can tell, the coolant flows down towards the electric pump and keeps the coolant from backflowing when the pump is off.