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It is nice to have a few manuals to play off each other! The '87 in particular has lots of weird first-year stuff that's not in the later manuals, including a just-different-enough-to-cause-problems engine diagnostic code table. Nissan also put the tstat on the cold side of the KA and the VQ, and Chevy did something similar on the LS V8s, so clearly there was some kind of thinking behind it. I have not found anything that explains what that thinking was. My best guess is that mounting the tstat lower means it's not sitting in the hottest water in the engine, so it's opening later, helping the engine come up to operating temp quicker (which is better for fuel economy, engine wear, and of course emissions.) But that's just a guess. Whatever effect they were going for on the VG, I guess they decided there was some meat left on that bone when they drew up the VQ, because it's even weirder. They still put the tstat on the cold side, but they also split up the coolant outlets for the block and the heads, which let them put a second tstat on the hot side of just the block.

Thanks, Slart! And thanks for the REAL diagram, you've been telling us for years to get the earlier FSM's as well, now I see why! They must've omitted the drawing from later ones to hide their illustrious "design" of the cooling system. (Tstat being on the "cold" side is well-stated!)

Nope! Other way around. Hot coolant passes from the engine to the rad via the upper hose, and cooled coolant returns via the lower. This is the direction in which the thermosiphon effect is pushing the coolant anyway, so it's how most cooling systems work. (There are reverse-flow oddballs out there, notably the GM LT1, but the VG is not on that list.) This means the VG's thermostat is on the cold side. I don't know why Nissan did this, but it seems to work. There's a flow chart (heh) on LC-6 of the '94 FSM, but this diagram from the '87 is a little easier to understand--at least once you work out that the grey arrows mean something different in the diagram than they do in the flow chart below.