Mercury 200 XRI random Overheating Alarm???

[Hess]

I've gained a lot of knowledge on this site and taken care of more than a few problems over the years (by searching). Thanks to ALL always!

A couple years ago I picked up a 1992 Mercury 200 XRI on a semi-rare 20' Concord Open bow and it's the closest to a performance boat I've gotten to (so far!). It's been a real blast and still works well for the family. Just installed hydraulic steering and now it's even better!

All this being said, I'm a little stumped on this a problem and not finding an exact match to the problem at hand (lot of close info though). The problem is last year I started getting miscellaneous continuous alarming. Before I learned better here that this continuous alarm is not oil (because it's continuous), I feared the oil injection from day one and even with all of the controversy I did the oil injection delete (again, through this site) and am pre-mixing. I'm not sure I disconnected the entire oil alarm (part of my confusion) as it seemed tied into the temp alarm as well (?).

I've got a water pressure gauge that shows ~12-14psi when running on plane (2-4 at idle). Looks like good flow from the telltale. Engine runs great for an hour or two or sometimes all day and then the continuous alarm goes off. Every time it goes off I shut it down immediately, wait 10-15 seconds, and the alarm is cleared, starts right up and runs great again... until the alarm come on again which seems to happen more often after it starts doing this (maybe every 10 minutes or so then). After shut down, if I don't wait 10-20 seconds and try it after 2-5 seconds sometimes the alarm isn't "cleared" yet and I wait a little longer (10-15 secs) and we're all good and on our way again. The fact that it's "clearing" with no more alarm after such a short time seems like it's not really overheating (?). I checked the temp of the heads (by hand) once last year and recall it wasn't screaming hot to the touch (but it was pretty hot).

So I'm stumped what can cause this and how to test or move forward based on the intermittent activity. Previous owners of the engine have done "stuff" like changed the water separating filter to a normal inline filter (who knows why) among other things... I never got the "test beep" when turning the key which also tells me something isn't right there (?).

I was going to pull a sensor and test it but there's no disconnect so didn't do it. Looks to be the single brown wire temp sender style fed right into "a terminal block" on the starboard side of the engine.

So, bad sensor(s), ground issue, faulty alarm module, actually overheating? Can anyone prescribe some further testing to troubleshoot this or are these symptoms obvious to any specifc problem?


Secondary Question: Seems like there's a consensus that temp gauges are no good but I'd sure like to have one in conjunction with the pressure. I see open ended blue and brown wires in the harness by the gauge cluster and also wondering if I could simply add a gauge with these wires? I think they may have disconnected one in favor of the pressure and a jack plate gauge which was gone and removed when I got it which is where I'd put it back in (to the non needed jack plate gauge)

Thanks in advance for any insight and advice!