phasor marinized kabota iverheats at speed

[Dave22q]

Older engine Kabota 1505E. After travel from Daytona to the Keys developed issue. Temp fine at 1800 and below but if I add throttle they rise to 200+ at which point I back off the revs and the temp drops to the normal 180-190. Several "mechanics" have checked the obvious but no joy. The last, after $1000+, was 'its because the water is warmer here'. Does anybody recognize this one?

[motion30]

Basics first. New impeller. And clean coolers and exhaust elbow

[Jolly Roger]

I agree, sounds like water shortage; Also check the actual water inlet pipe from the seacock. I found mine to be half constricted, down from 3/4" to less than 1/2"