Had the same problem on my 8BA. Foaming is caused by worn water pump seals. When running, the inlet side of the pump is under av slight vacuum. The worn seals allow air to be sucked into the system, causing the foaming. When the engine is shut off, there is no vacuum being created and the seals re seat, thus no coolant leakage. If you want more info on the subject, e mail me at
[email protected] or call me at 705 439 2567 or 705 934 4434(cell)