ok, it is probably just air, but the 350 is running at 240+plus, and it never reaches a plateau. it just goes up up up! I put a perma cool 16 inch HP fan, that pulls 2950 cfm, we use the stock 305 radiator, but it is the same pn as the 350 radiator, we had it flow tested and rebuilt just to be safe. The 350 has a Milodon high volume steel water pump, and a 160 degree thermostat. My dad says the fan I bought is probably too wimpy, if anything, but we both seem to think it's just air. Do I have a weak link?

 

The fan CFM should be more than enough.

Is the water pump turning the right direction? If it's a reverse flow water pump and a standard fan then that will cause a problem. If the Mildon is standard direction, is the belt making it go in reverse direction?

Is the thermostat opening?

The rad was rebuilt so it's not plugged.

Take some timing out of the ignition and try again.

Try a different thermostat and sending unit.