169 isn’t hot I don’t think.
Your saying it’s alarming at 169?
If not, how hot is it when it alarms? I’d try a thermostat, easy and cheap. I really don’t think that is it, but easy and cheap to eliminate and you may get lucky.
The air bubble thing can be tricky, it moves around and causes trouble, I assume it could move into the
water pump and make it stop pumping water.
Again, see if it has a bleeder screw and if it does open the screw and with fresh water cooling system full it should flow out
coolant, but it has to be completely full as the bleeder screw ought to be real close to the top of the system.
I’m sure googling how to bleed a Chevy cooling system will show you how, assuming the
Marine engine is reverse flow, and has bleeder screws.
My old 454’s didn’t, but likely they were too old.