I found that my radiator was catching debris from the block since the car had sat for many years by previous owner. I changed the thermostat and flushed the radiator several times. But what worked best was to connect a hose to my shop vac and vacuum out the radiator to clear the fins. Flushing helped but I could see gunk sitting in the fins. It was sold material and came out nicely that way. Mine runs cool now and I do not have a fan shroud on my 64 valiant. Though I would if I could fine one local and cheap enough.