Re: Motor too low causes backed up exhaust?

[Don]

Is this the same engine we were discussing in a recent post??
Well, having an engine too deep in the tank, or on a boat with a low transom surely increases exhaust back pressure and can adversely affect low speed running quality. I don’t really think that pent up exhaust is sneaking into the water pump though (unless the pump isn’t sealing properly).
On the other hand, we all know how an test tank can affect running quality, and create air/exhaust bubbles in the tank which may get ingested into the cooling water intakes creating a cooling problem.
Have you run the engine on a boat to rule out test tank headaches?
So, you are saying the engine will cool just fine if left in neutral, even if revved up slightly, but will stop pumping once put in gear and the throttle is advanced a bit. Do I have it right??
Once test tank issues have been ruled out, I am still thinking that there is a sealing problem with the water pump/shift rod oring.
The engine will cool fine if left in neutral because the pump is immersed in water completely. Once in gear, with some throttle applied, the water level drops below the water pump allowing air to be drawn into the water pump.