[Fr. Frank]

But what do you think would cause the intermittant pulsing of the water coming out? My guess is a bad blade on impeller.

No, it's not a missing impeller blade. Even with two adjacent blades missing, you would be unable to detect any pulsing in the flow of water, as the impeller simply rotates too fast.
Pulsing in the flow of the telltale is either thermostat or poppet valve.

Some think I am overly careful, but I replace my impeller every January, or every 100 hours of use, without fail. I advise all of my friends to do the same. Waiting for your water pressure to fall away to nothing before changing the impeller is like waiting for your oil pressure to fall away to nothing before checking or changing your oil. By the time the pressure falls, damage may already be occurring.

$18 for a new impeller is a cheap insurance policy. I have never lost an engine or powerhead to overheating in 41 years of boating, including over a decade in marina management. On the other hand, I have seen LOTS of outboard failures caused by NOT changing the impeller regularly.

I also have a mechanical water pressure gauge, even though my Optimax Smartcraft system has an alarm if the water pressure falls below 6 lbs.

Bottom line: change the impeller, change the thermostats, change the poppet valves. It's the right thing to do.