Steam at the overflow hose below the radiator cap?

Bewy said

That is NOT normal. It sounds like there is a leak in the cooling system. Examples: external leak, such as a freeze plug, or internal such as a leaking head gasket.
As the volume of water depletes because of the leakage, there is not enough water left to cool the engine & temp rises until the coolant boils [ steam ]. That is the steam you are seeing.

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I have to agree. If the radiator was filed to the top, it would spill some coolant at shut down but not a gallon. A failed or low pressure cap along with clear water could cause it to loose more over time. If it is a head gasket, the copper colored liquid head gasket fix from Barsleak really works. It cured my 96 4cyl. Camry with same symptoms over 2 years ago. Only time I could see steam at the tailpipe was at cold start and that wasn't much. Its close to 293000 miles now.