So, I've been having problems with my exhaust elbows overheating (I have another thread going on this). Long (very long) series of tests led me to questioning the raw water pump. From what I hear, the pump should be producing 24G/min @3000 rpm in-situ. If I bypass EVERYTHING, i.e. 1-1/4" ID hose feeding the pump directly from overboard (made as short and as straight as possible, definitely less restrictive than the VP preformed hose that goes to 1"ID at the oil cooler and even smaller inside the outdrive intake) pumping to a bucket through 1"ID hose (again, as short and as straight as possible), I see only 19-20G/min @3000 rpm.
Now, my pump is P/N3857794, i.e. old style pulley-driven pump. It looks like Volvo switched to a new style (crank-shaft-mounted) pump around 1999, e.g. P/N 21214596. The key difference that I see is the configuration of the incoming and outgoing pipes. The new pump appears to have much better design to support centrifugal type of pumping. Here is a quote from VP workshop manual:
"During low speed operation the impeller functions as a positive displacement pump. At higher speeds it functions as a combination centrifugal and positive displacement pump. The shape of the housing and/or liner cause an eccentric action
of the impeller blades during engine operation. During periods of high speed operation, the resistance of the water on its way through the pump is sufficient to prevent the ends of the impeller blades from making contact and following the inside perimeter of the pump housing. The blades merely flex in toward the center of the impeller to perform as a combination centrifugal and positive displacement pump."
So, it looks to me like the new pump ought to have better pumping characteristics compare to the old one. Is it really the case? If so, is the 24G/min@3000rpm number more relevant to the new pump?
Another related question: can I upgrade to the new style of RWP? What would be involved?
Now, my pump is P/N3857794, i.e. old style pulley-driven pump. It looks like Volvo switched to a new style (crank-shaft-mounted) pump around 1999, e.g. P/N 21214596. The key difference that I see is the configuration of the incoming and outgoing pipes. The new pump appears to have much better design to support centrifugal type of pumping. Here is a quote from VP workshop manual:
"During low speed operation the impeller functions as a positive displacement pump. At higher speeds it functions as a combination centrifugal and positive displacement pump. The shape of the housing and/or liner cause an eccentric action
of the impeller blades during engine operation. During periods of high speed operation, the resistance of the water on its way through the pump is sufficient to prevent the ends of the impeller blades from making contact and following the inside perimeter of the pump housing. The blades merely flex in toward the center of the impeller to perform as a combination centrifugal and positive displacement pump."
So, it looks to me like the new pump ought to have better pumping characteristics compare to the old one. Is it really the case? If so, is the 24G/min@3000rpm number more relevant to the new pump?
Another related question: can I upgrade to the new style of RWP? What would be involved?
