Impeller operation question

[cgrooves]

I attempted a brief search to no avail. Sorry if this has been answered a million times. This is my first season with an I/O, so I'm just learning.

What 'drives' a raw water impeller in the outdrive? (i.e. Is it gear driven?)

I had thought that perhaps it was driven by the suction created by the circulation pump on the engine, but if you disconnect the hose coming from the outdrive impeller at the thermostat housing it continues to flow water, so that tells me that the circulation pump suction isn't 'driving' it.

 

[Don S]

Re: Impeller operation question

The pump impeller is keyed to the vertical shaft in the lower unit. The vertical shaft is basically connected directly to the crankshaft of the engine thru the gears. Anytime the the crankshaft is turning, the water pump impeller is turning.
The shifting is done in the lower unit.

 

[Fishermark]

Re: Impeller operation question

It simply slides over the main driveshaft in the outdrive. As the shaft turns, it turns. It is offset in the pump housing which causes the vanes to flex and pump water:

EDIT: Don was too fast.