I need first to check raw water flow in the system --at the exhaust, at the pump output, before heat exchanger, and before injection elbow-- BUT a marginal R/W pump is entirely possible, which I hadn't realized (since they look very simple).

I bought my engine rebuilt (for the most part), but I don't think the raw water pump was replaced (had new rings, big end bearings, valves, valve springs, etc. replaced), and it was done in a shop, so professionally done. However, prior to rebuild, the engine had been on a boat in the Caribbean charter trade, so perhaps the engine was used hard, and now the raw water pump is worn out and marginal? I was told by Volvo today that, after many years of service, the impeller vanes slowly wear away the inside of the pump housing, resulting in less and less suction power since they contact the pump housing less. Makes sense; hadn't thought of that, that the pump could be worn out.

FYI, about two years ago, I replaced my impeller cover with an easier-to-remove SpeedSeal (www.speedseal.com , which has knurled thumbscrews instead of teeny-tiny screws). As far as I can tell, it fits fine, and not too tightly. Perhaps I should loosen it a bit when I'm checking raw water flow, to be sure it's not binding on the impeller.