Anyone have any good ways to clean out a partially plugged radiator without removing it from the car? My 49' is overheating on the highway suddenly. It was fine for a week, and then suddenly on the way to Mokan it started overheating. Its running a little rich, timing is set to 36 degree total on the 262ci v6, and its using a V8 rad from a 74' Dodge dart, and an electric fan. I thought the thermostat went bad, so I removed the guts from it and its just acting as a restrictor. There are no leaks. The water looks like rusty mud now, and I think its all from the block. I have flushed out the block with a garden hose now, but I think the crap has partially plugged the raditor. I am thinking or trying a gallon of white vinegar in the cooling system for 15 minutes then draining. Anyone have any other solutions?