Sounds like a frustrating experience, Bill.
I agree it sounds like possible air ingress on the suction side [assuming the new impeller is working as expected...]
Looking ahead to future changes that may be of interest...
Two boats ago I started plumbing
my raw water
wash down pump output [Ts with valves...] into the raw water suction side of all engine coolant
loops as a back-up and primer. This has paid off a couple of times in critical situations, but doesn't work as well if bits of impeller block coolant
On our current
boat we have a Panda 10kw generator
. It has had both the alternator
and water pump replaced with external sources. (i.e., no belt...)
is just an idler pulley in case a belt driven water pump is of interest in the future.
There is no need on this boat for a generator
alternator as when there is AC available [or the main engine is running, it is sunny or windy...] all batteries are being charged.
Why no water pump either?
When the manufacturer had a batch of bad impellers years ago- but didn't admit it until 6 months later- the previous owner bypassed the built-in water pump replacing its function with a spare 110VAC March pump [used for the raw water coolant loops for the air conditioning
systems.] Ten impeller changes in 2 months would make me re-engineer that system too...
He also relocated the heat exchanger
to outside the generator's acoustic housing so it could be replaced with a larger exchanger [and is more readily serviced... They were in the tropics at the time...]
These changes make everything much more serviceable and provide redundancy if one wanted to put a belt back on to run the built-in water pump [with a functional impeller...]
We don't hesitate to properly [and cautiously] re-engineer [optimize] systems using standard components, methods, and procedures, but only when necessary... [Who needs to make more work on a boat?]
I look forward to learning
what is keeping your pump from working as expected. And for your sake, I hope that is soon...