This is one that I went through last winter, and just tested it in
the barrel today.
I didn’t think I was even going to get it started, as it pulled over
so stiff.
It finally started, and seemed to pump water okay for a few seconds
while watching. After playing around with it a little while later,
I see “Zero” cooling water discharge, but upon restarting,
it pulled over a lot easier, which made me think the impeller
drive pin failed.

This motor ended up with a Sierra impeller 18-3072, which was a
good diameter, and correct shaft size. The impeller was a little “short”
though, and I machined down the ss liner to match the impeller.

There’s a flat on the driveshaft on which the impeller drive pin is located.
I had to make a drive pin, and ended up using a piece of brass rod,
filing a flat on each side to make it fit.

In turning the driveshaft over by hand, it appears to be driving the impeller
okay, but perhaps under power it was slipping, but I didn’t see the
plastic hub on the impeller chewed up.
Just made a mental note to check the hub tomorrow and see if it’s cracked.
I found nothing obstructed in the intake of the pump.

Q. Anyone have issues like this, and what did you figure out to be the problem?

https://youtu.be/PSyDuEiUqXg