After a drive the other day, I noticed my '36 sedan spit a bit of coolant out of the overflow tube, which it will do if the radiator is overfilled. I pulled the cap while the engine was running and the coolant was very frothy, which is why some came out. Is this a symptom of a blown head gasket? The car does not overheat nor has it ever boiled over or anything since I restored it. I ran some Thermocure block and radiator cleaner through it last year and replaced the coolant with fresh stuff, so it should be spotless in there. Maybe residual cleaner is what caused the foaminess?
To try and gather some more information, I disconnected the belt so the fan and water pumps weren't spinning and ran the engine up to about 190 degrees F. As it got up to temp, I saw some small bubbles coming up through the driver's side radiator hose (the only one you can see through the radiator cap). They were small in size and quantity but visible. Is this air or steam?
The car uses no coolant, none of it is burning as there's no smoke or stinky exhaust and all the spark plugs look perfect, a nice dusty brown. Do I have to replace the head gaskets?