I think I see your point. The likelihood that only one cylinder would have a valve open and three other cylinders with closed valves would be nil. There are 4 cylinders on the bank with valves at some point of activation, unless there are three cylinders in the "power" stroke at once. The more overlap the cam in the engine has, the more pronounced this should be. Not likely there would be just one cylinder with an open valve. This is what causes me to question the integrity of the water jacket around that particular cylinder.