Sorry if I did this wrong but this is my first time posting.

I have a 502MPI inside my 1991 Baja 250es. I have had the boat for 2 seasons now and never had any mechanical issues. But as of last weekend I started to overheat when on plane, but cool down to normal at idle. Before this issue the temp would sit between 160 and 175 depending on heat of day and time of the year. Until last weekend, at idle it will sit at 160 but when on plane at 3000 rpm or higher it slowly creeps higher and higher Till I come back to idle. I try not to let it get past 190. But I hate doing this heat cycling to the engine.

Instantly changed the old water impeller and housing for water pump. (I have a surface pick up on transom, pick up on bravo 1 drive wasn’t enough)
checked for leaks - no leaks found
replaced my “pro flush” system with a price of straight pipe to eliminate chance of sucking in air
tightened water pump v-belt
i also considered the TStat being bad. But when engine temp would get abouve 190 I noticed an immediate drop in oil pressure (tells me that the oil is actually getting hot)

Did all that above and still having the same issue

i plan on back washing the engine and oil cooler tomorrow before going back out on the water. But what do you guys think it could be?

Ps. When removing old impeller it was it crate shape. No broken pieces!
ps. This boat hasn’t been in salt water for 3 years. Not sure if it matters but I thought I would through it in there.

thank you for your time and support
~Tyler

I would say thermostat, exhaust or stuff blocking cooler. You can start by backflushing the coolers. Replace thermostat. If it still does it it’s likely exhaust/risers