So people are always having issues with impeller chunks and fragments plugging chit up downstream and i now may be one of them . Why on earth hasn't someone made and promoted a clear post pump filter screen to attach directly to the pump, so one you don't have to clean debris out of coolers and thermostats, and as a bonus you can look in and see that you're impeller is is intact.
mods please move this post I'm not sure how it landed here.

Ya, like the little glass fuel filters.

Yeah similar with a course mesh so as to not create a restriction.

On an old boat, I even contemplated installing an old oil cooler (no oil plumbed to it), right after the pump - that I could access and clean out a lot easier than the PS pump (access on the 502's were difficult). Kinda like a poor mans strainer.

Boating on a river, beaching the boat - will all spell bad news. Those small river pebbles get lodged in the cooler tubes and won't come out with backflushing. Gotta get a welding rod or coat hanger in the there and push them out.

I've cleaned more oil & PS coolers than I can count !

They make sea water strainers, alot of the HP boats have them.

I believe they are designed to go on the suction side to keep debris from reaching the.pump, not sure though.

yes they are but they can handle pressure also. That is a good idea, but hard to find space for them in some boats. I installed water pressure sensors on the intake side of my intercooler, pressure at cruise has risen slightly since I installed them a few years ago, I am planning on pulling the motors this winter and cleaning out all the raw water system parts.

I like that idea a lot, would have to relocate my power steering cooler to the other side after the oil cooler which makes more sense to me anyway.

the oil cooler does a good job of this

^^^^ correct internal oil coolers most are honey combed and catch pieces on the backside. Easy removal is you pull off front and back side of the oil cooler hoses and stick small diameter rods (we use inters of cut to length OMC throttle cables) thru from front to back pushing out broken pieces from each honey comb section. . Also we use picks on the backside and stab pieces to pull out. .

Keep the broken pieces and match up like a puzzle with the impeller you just pulled out of the housing. If you are still missing big chunks then you know keep on searching. If your puzzle is completely (broken impeller) put back together then you know you retrieve all the pieces.. Just saying