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For what its worth, it may be the engine scale is high or partially clogged as was in mine-would constantly run 210 and spit up at idle. I used a Rydlyme descaler in my engine block-set up a pump (Harbor Freight) to circulate it for 24 hours, (careful, its lightly caustic )then flushed flushed and backflushed the block with a garden hose sprayer. Then put in vinegar, ran it a few times hot to cold cycle, then one night to sit, then got it hot and drained it, then flushed flushed flushed with clear water. An engine rebuilder said he thought the block was plugged or obstructed, and he was right. I now run distilled water and a bottle of Rislone Hypercool, now it runs 180 even on extremely hot days, no overflow. Maybe you already checked the timing and the radiator to be sure it had good cooling flow. FWIW