My Austin seven has had the same honeycomb radiator insitu for at least 60 years that I am aware of but recently I had noticed that the engine was getting hotter particularly  on summer days thus it was time to either change it or explore cleaning it out.Over a period of time I enquired with a number of people if they could provide some advice as to whether the core could be saved by cleaning or just bite the bullet and replace it with a new one. Every opinion was either it probably cannot be done or use an aggressive cleaner and hope for the best, this idea was dismissed as I considered that they could damage the copper and solder etc. I was also reticent to take the core to a radiator repairer as only the year earlier they had damaged one from my other Austin beyond redemption due to applying air pressure beyond a safe limit of 2 psi.Research continued and with the core removed from the car I thoroughly flushed it out with a garden hose which moved some gunk as a plan ‘A’. Plan ‘B’ was a tad easier, with the core lying flat and the holes ready to be sealed up I filled the core with white vinegar which I purchased from the supermarket. I allowed it to munch away for 24 hours and flushed it out then repeated  the process a second time and the result was excellent and no damage to the core either.The product can be reused but not in the kitchen of course.