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Just thinkin outloud here.. 

I found all 4 valves.  I ran the Aquahot preheat today to try to isolate the Aquahot loop to see what valves warmed up the fastest with no real concrete outcome.  Valves 2,3,4 warmed up and 1 was cold.  

From what I’ve read about semi’s with 60 series motors is that the inlet to the heater core is up my the thermostat (valve 2) and the return is on the suction side of the back of the water pump (valve 1).

Valves 3 is almost impossible to get to. I need longer arms.  Once they go over the transmission I can’t see where they go.  

I’m going to close valve 1 and 2 and fire it up to see if the aqua hot still heats up.  

Let me know what you guys are thinkin

Sorry Dennis, somehow I missed this post. 

So I will have to go look but I am thinking that valves 3 & 4 are on the pressure or supply side and that valves 1 & 2 are returns. But it’s hard to see in the photo. 

Here is my reasoning and understanding of how the S60 coolant flows:
Coolant leaves the pump (output flow) and goes into the oil cooler, thats the housing just above the oil filters that they attach to. From there it goes into the block, flows up to the head at the thermostat housing. At the thermostat you have two paths, a bypass right back to the water pump the other path is to the radiator (when the thermostat opens). Radiator then has a return line to the water pump. 

So this is why I am thinking that valves 3 & 4 are on the output side of the water pump because it appears they are coming off the oil cooler. That would then leave the other valves 1 & 2 as returns. 

I will try to remember to look at mine this afternoon when I get home from work and see if I can see where those valves are connected.