You can look inside radiator for evidence of corrosion and plugged cores. When engine is running (safer if recently turned off), feel around radiator for "cool spots" that indicate no flow of coolant thru a section of cores. What size fan you got? I've got a 16" electric pusher and no mechanical fan on a '60 235 in a '54 bel-air. Keeps it cool with a 160 deg thermostat. Check water pump, thermostat, coolant mix, and for corrosion in water jacket of head or block.
What year 235 you have? The '55-62 2nd series engines had better water pumps/water jackets than the '53-'55 1st engines.
Ignition timing (base and advance curve) have a lot to do with overheating under load. So does octane of fuel used and fuel delivery issues (carb jetting/adjustments, vacuum leaks, etc)
chip
