M103 Cooling system flow direction
 

So I was looking at my cooling system and put my aux water pump back on after I had it off for some years, but after looking at how it is supposed to be installed, it doesn't make sense. The hose connecting the aux wp to the coolant pipe going to the belt driven water pump shows that the coolant flows from the aux wp to the pipe. However, the other hose from the aux wp goes to the hose leading to the heater valve and heater core. So shouldn't the aux wp be pumping the coolant towards the heater core? I assume it should flow that way because the heater valve is there to block the flow of coolant when no heat is needed. I bench tested the aux wp and the water flow is indeed going in the direction of the belt driven wp and there is even a small arrow stamped on it that shows which direction it flows. Anyone have any intellect on this or am I missing something? This isn't the first I've noticed that there seems to be a mistake or fault with the MB design. The EGR valve with the check valve is another that has always baffled me, but no one seems to be able to explain that either. Hmmmm

And there it is.

If your rad is metal,you can have a shop add extra rows for better cooling.

The water pump has both an intake and a discharge. Just because it goes "to the pump" doesn't mean it's on the discharge side.

Does the heat work? If so, it isn't wrong.

Coolant leaves the engine by the oil filter, goes through the heater core then goes through the monovalve for flow control. Yes, the heater core can get hot when you don't want it to, such as when parked after a drive on a hot day. That's how MB made it.

Where is this EGR check valve? AFAIK there's a simple vacuum actuated valve on the forward exhaust manifold connector then a pipe to the intake manifold.

Sixto
98 E320s sedan and wagon

If the coolant leaves the engine by the oil filter, then goes into the heater core, wouldn't the heater valve be on the side where the coolant was entering the heater core and not exiting the heater core? I've never been able to get a handle on the air flow for vacuum or the coolant flow of the m103.

That’s how I’d design it but not how MB made it.

Sixto
98 E320s sedan and wagon
02 C320 wagon

help
 

This might help its for the M103 .

It doesn't really matter where the valve is as long as it completely blocks flow to the core. It was probably a matter of packaging that it ended up on the downstream side.

Duke

You would want the valve and aux pump on the outlet of the heater core so they see lower temperatures. After all they are plastic with rubber components and higher temps would lower their life.