Before I Drill a Hole in my Boat.................

I've ruled out a list of things that may be causing my "high speed overheat" (thanks to the help from here)

im on the verge of installing a Buck Algonquin Though Hull Water Pic k up on my 2000 Mercruiser 5.0 with a Bravo 3. 1800 hours. I have done the following.
replaced Manifolds and Elbows both sides. (They had 1500 hrs on them)
Replaced impeller with OEM Mercruiser complete kit. (It was completely intact)
Replaced aluminum exhaust tubes (both)
Pulled off covers on Heat Exchanger fairly new and completely clear.
Power steering oil cooler clear
Thermostat opens right at 160 and stays there till I run the boat at 3800 RPM for several mins.
Then it goes to about 172/175. Throttle back and within a min or two right back to 160
Verified with IR Laser at hose going from outlet of thermostat housing to Heat Exchanger to be 172 when hot.
I've been reading a lot about "Bravo-it is" If I do choose the Through Hull route is there any negatives to using a Tee to connect the existing hose to work in conjunction with the new Through Hull?
Is there anything else that I am missing?
thanks so much!
Rick

Have a customer with the dual pickup so it does work. The drive is cooled by the water flowing thru it so keep that in mind.
Have you checked the hose connections for corrosion closing off the watrer hose?

No I haven't , very difficult to get to, I'm assuming that is the problem and that's why I'd rather do the through hull than to have the boat pulled at the Marina and start that process. My boat is on a lift and to do the through hull would be easier.
thanks so much for the input, I appreciate your time.

Did you clean inspect the heat exchanger and or oil cooler? Get a preventive maintenance list and make sure everything is up to date!

If you have power steering pull the cooler on the back of the motor and just replace it if it is past its life expectancy.

FWC Bravo 3 drives require a thru hull water pick up. If you want you can cap the transom line and cut the water hose in the bell housing.

WHats wrong with 175 degrees with a thermostat of 160?

My 143 degree runs at 160 when at high rpms all day every day and when below half throttle it stays pinned at 150 all day every day.

So 175 temp is a 15 degree increase is normal in my opinion at higher rpms.

If you break 180 and stay there then you "may" have issues