I don't understand the March pump inline with the mechanical one.
Reason is that most likely if a generator
water pump is going to be damaged its during the initial dry run until it primes, and I'd assume that where a Cat usually mounts a generator
is even higher than average for a mono, so more likely for a dry run and a longer one.
But the March pump will not begin to pump water until after the generator is putting out AC power, so your still going to have several seconds of dry run, every time and damage is cumulative.
But if you used a DC pump it could be wired like the electric fuel pump
and or the DC powered ventilation fan if you have one, to come on with ignition and pre-prime the mechanical pump. Just know of course that just like your main engine if you continue to crank without starting, your muffler
will fill up, maybe faster so be wary.
But, why have a mechanical pump at all? Or if you don't want to re-plumb, just simply remove the impeller of the mechanical pump and let the March pump supply cooling
Yes you do have the first ten sec or so of no cooling
water, but nothing is going to overheat in such a short time.
I am not a Cat, but had trouble with my Jabsco pump and didn't like the consequences of the failure, so I eliminated it and went with just the March pump, so far works great, don't see any downside, and I think there are many like that, seemed when I asked here the response was that there were many like it, go ahead.