I doubt that these cars would overheat in the same circumstance when new. I would flush the radiator, change fluid if it hasn't been done in a while, clean the radiator and evap with the radiator removed and replace or at least test the thermostat. I do't like to be stuck on the road and consequently refurbish the entire system when it goes out.

Make sure that hoses aren't at the end of life while you're at it. Then the thing will cool. Radiator fluid needs to be changed to keep electrolysis from eating the heater core.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.