Mercruiser Temperature Issue

[daceman63]

I have an issue with the temp on my 1993 350 260 hp mercruiser engine.
-Bravo drive
-New Belt driven raw water pump
-The second New thermostat
-removed risers and manifolds and all are clean and water runs through freely
-the risers are stainless and look really clean. Teh manifolds are 2001 but there was no blockage or buildup at all....
-At idle the Temp fluctuates from 140 to 165. Engine heats up to 165 the thermostat opens and cools to 140 and the cycle repeats itself.

I've owned the boat for 8 years and she has consistantly run around 150 to 155. I've never had that much fluctuation in my temp. Is there an issue?

Could there be a restriction in my water flow?

Thanks for any info.....