Lets see if I can answer the questions:
David- What boat is this on ? It is an 89 bayliner 2755, 27 foot, 454 with bravo out drive.
Have you aimed an IR gun near the thermostat housing when the gauge reads 200*F, as a reality check? Yes, guage and IR gun read the same at all temps.
People on board, same going out as comming in and in the same seats too. Actually move people to the bow in the cabin when it did this to see if that would level it off, made no difference at all.
have you put your hand on top of the riser/elbow to see if it remains cool or cool enough you can keep your hand there indefinitely without pain, to tell you whether or not the RW side has sufficient flow? no, have not done this yet but will once the risers are back on.
Was this engine always FWC cooled or upgraded to FWC from just RWC at some point? Not sure, it looks like it came with the boat and was not an up grade, but I really dont know and cant tell from the maintenance records as it was not in there.
Any chance the A/F had mixed green with red ( old -type with long-life type)? Not sure, possible but I doubt it as the PO left 2 bottles of green in the boat.
Or had salt RW gotten into the FW side at any point ? Been in fresh water its entire life as far as I know. It originated in seatle but was not there long and was not registered there so it is doubtful it has ever seen salt water, likely not in the engine for sure as I bought it with 115 hours on it.
It sounded like you said you were running undiluted 100% A/F in there for awhile. Is that right, or was it the 50/50 % type that got further diluted? I dont have a tester so I really dont know, it looked pure, but again no way to know for sure. I have added a lot of straight water to make up for the loss of taking all the stuff off, as did the marina, but I dont know the exact level yet.
Some ignition systems have a 'Limp Home' mode in case something is going wrong. Might be oil/pressure related or temp related. You'd have to investigate your system. No ecu so I doubt there is a limp mode, oil pressure looked good at 40psi, and I could easily get 3k rpm, just could not get it over the crest. Just weird it was in the same spot both times with equal number of people and should be less weight with the fuel burn.
Forgot to talk about your balls...the ones in the thermostat housing. Someone might have tried stretching the springs thinking it would run cooler when it does the opposite. Try getting new balls and springs. No balls and springs in the housing, it is a simple housing with 2 sending units and 2 hoses, all open holes. Enough about my balls
I boat and store in an area prone to freezing temps so pure water is not an option, changing it out each year could be, but a difficult task since there is a lot of lines and a lot of antifreeze. It has 2 external heat exchangers, one in the front of the cabin for heating and one in the water heater also.
Yes it is true that I dont know the exact mix level, but I have lost over 4 gallons of antifreeze and replaced it with water, so far. I would guess it is on the lower end but I dont know that. I guess I need to buy a tester and know for sure just where it is.
Yes it has been like this since I bought it, and did not think much about it. Still wonder if I am chasing a goast as it never gets over 200, even at full throttle on a long run, stays right there, IR confirmed. Agree with a 160 thermo it should get no more than 170, but.....
Would the river water temp have anything to do with it? I dont know what the exchange rate is, but the river was 85 to 89 degrees. Not sure what kind of drop I can expect to see.
Thanks guys.........D........