2006 four stroke 75 Hp. There isn't any visual indicator stream coming out of the back of the outboard. I have taken the lower unit off multiple times and checked the water pump. Put in a new impeller, still no flow. Checked exploded view to make sure everything was there and in the proper order. Tried flipping the impeller over just to make sure the vanes weren't backwards, no help. Checked the hose for a plug but all clear. I have changed the impeller before and had no problems. Is it possible that the thermostat is causing the problem?