andrei, instead of a temporary Rube Goldberg fix bite the bullet and replace the radiator. It will need to be replaced eventually and you'll avoid getting stranded somewhere at the worst possible time. You can buy a new Behr radiator for your 300E at benzautoparts.com for $182. Consider replacing the thermostat and be sure to use either MB coolant or Zerex G-05.

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Fred Hoelzle