When gasoline burns, since it is a combination of hydrogen and carbon, the result is carbon dioxide CO2 and water H2O. The carbon combines with oxygen to form carbon dioxide and the hydrogen combines with oxygen to make water. That is where the white stuff on your oil fill cap came from. It's water. All engines have combustion blowby and this blowby has water in it and it shows up on the fill cap especially on high mileage engines. This is not usually a concern.

When an engine first starts up, the exhaust system is cool and it condenses this water in the combustion products and it runs out the exhaust as liquid water or vapor. So, be sure that this is not what you are seeing coming out the heads. It just may not be coolant. If you have that much it probably is though.

 

Did you check the block? If it isn't flat coolant can leak into the cylinder from there. Were any of the plug ground electrodes white?