Why is my radiator bubbling over?

A line of small white foam bubbles have started to appear all along the lower edge of my radiator. Although the expansion tank level has not really dropped, do I need to consider Radweld or a repair?
Anon

If it was a leak along the bottom of the rad then the tank level would be on its way down rapidly. It’s far more likely to be corrosion bubbles caused by road salt reacting with the alloy material. If you carefully clean it off and repaint the rad it should be fine for years to come.