My cover was scored (circular, from the impeller wearing it) enough that you could see it easily, and catch it with a fingernail - maybe 1/32" - 1/16" or so.
Yours sound OK. I am not a mechanic, so maybe someome else can chime in. I think that if your raw water pump
and impeller are in good shape, you shoudl not have water or air bypass it. I don't think any air leaks are good. However, air is always in the exhaust
elbow, yet doesn't make it's way back through the heat exchanger, and then water pump
. Your possible leak is quite far down the line
, so it may not be an issue. I do think any leaks / loose clamps near the pump
would facilitate the loss of prime.
Let us know how you make out.