The next step to making these radiators functional was to route the hoses, which at first glance seemed like it would be a simple task: a supply hose here, a demand hose there, a couple of tees, and voila. Except I simply couldn't figure out which of the pump outlets on the Northstar was for hot and which was for cold water. This was the best the internet had to offer:
It appears to be quite complete but it offers no details around the pump area, not to mention confusing arrows and coloured fluids not shown in the legend. Other sites offered contradictory statements by people who were as confused as I was, so that wasn't reassuring. Part of the problem was my stubborn belief that all engines run their hot water "out" of the thermostat to the radiator, when in fact, the Northstar does the opposite.
When I finally figured out that the thermostat controls the entrance of cold water into the engine, things started falling into place. Here's my schematic showing once-and-for-all the flow through the various coolant ports on the Northstar water manifold:
I'll explain it, not for the benefit of the poor internet soul of the future, but for my own future self trying to remember how it works. And that could be as early as next week! Starting at the water pump, cool water is pumped to the engine block through the lower legs of the manifold, where, through internal passages it flows to the cylinder heads. By the time it exits the heads and re-enters the top ports in the water manifold, it's hot. (The manifold has internal passages that keep the hot and cold water separated.)
Once back in the manifold, the hot water gets directed to several places: the cabin heater; the throttle body for anti-icing; the radiator to be cooled; or through an internal passage (pink arrow in drawing above) that routes the water back into the water pump to be recirculated through the engine if it's not hot enough. The combination thermostat/recirc valve is the brains behind deciding whether to recirc the water or send it to the radiator:
The pink oval in the drawing represents the recirc valve which stays open as long as the water isn't at operating temperature. Once the water is hot enough, the recirc valve closes and the thermostat (blue oval) opens forcing most of the water through the radiator (some of it can always go to the cabin heater and throttle body).
The cold water returning from the cabin heater and throttle body (blue dashed lines) bypasses the thermostat and the recirc valve entirely and is sucked directly back into the water pump inlet.
Of course being absolutely certain of the operating principle would have been an asset before attempting to make my first set of scale plumbing layout drawings. But I didn't, so I spent scads of time drawing in two views what ironically was the correct configuration, but then was convinced by an internet article that I had the flow reversed. So I deleted the drawings and re-drew all of the plumbing the wrong way, only to discover of course, the first way was correct. Did I mention I spent scads of time? Anyway, here is the final product showing how I planned to route the plumbing from pump to the radiators in the top view:
The combination water pump/manifold is in purple. The hot water is shown by the red hoses and the cooler water by the blue hoses. There are a couple details worth mentioning, for example, the long straight portion of the hoses heading from the tees to the passenger side are hard up against the firewall. The firewall is sloped at 20 degrees so it appears as though they're staggered in relation to the wall but they are in fact up against it at different heights.
The other noteworthy detail is that the hoses running from the tees to the driver's side were deliberately stepped away from the firewall to make room for the gas filler tube which has to pass in the same vicinity to connect to the tank.
Here's the rear view of the same thing:
I purposely kept the plumbing high along the firewall to maximize the space for the exhaust system later on. Though I may regret that decision when I try to bleed the system of air!