[apbright]

Foaming used to be a frequent problem for me, on two different cars. This happened even when doubling up on the rubber radiator cap gasket and double-sealing it with Permetex silicone adhesive.

Ultimately, I found my causes to be, on different occasions:
a) Residual radiator flush cleaner in cooling system
b) Rust from engine block, lodging in radiator tubes, causing poor flow through radiator
c) Overheating, as a result of heat (100ºF outside temp), uphill driving, and a more mild amount of (b)
d) Suspected, but never proven, head gasket leakage, while using the 'Premium Head Gasket,' i.e. Snyders part no. B-6051-M (it seems there are clear, conflicting experiences on this gasket design)
e) Overheating as a result of coolant loss through radiator leak, preventing proper water pump operation and thus proper coolant circulation

Since switching to the 'Best' graphite gasket (i.e. Snyder's part no. B-6051-XO), and having my radiators cleaned in one case and re-cored in another, I have not had these problems.

-Andrew