If that we're the case,you'd Freeze Your Wallet Off in January on I-285.
(I believe that Auxiliary Water Pump is on all the time the Key is On.)
The Mono-Valve regulates how much ,If Any, HOT water gets to the H.C.

They installed the Auxiliary Water Pump to "Make Up" more Heat availability
at Idle/Super-Low engine speeds (the Mechanical Water Pump is subject to
engine RPMs)...Look at all the Damn places the coolant has to travel on a
W124 chassis...Easily an extra 100Ft. in addition to cooling the engine.
(Distance/Friction=loss of flow rate)

__________________
'84 300SD sold
124.128