[mitch48]

I am in the process of flushing and refilling my Cayman with coolant. I drained almost all out of it, and I put in about 1 1/2 gallons and started the engine to warm it up. Before it got to operating temp, while I was holding about 2000 rpm, I heard a muffled "whomp" from the engine, so I shut it off, and white smoke started pouring out of the right engine exhaust vent on the side of the car. A small amount of coolant was evident on that side of the engine. I let it cool off and eventually got about another 1/2 gallon in the system. I've run the engine twice more, bringing it up to operating temp (145-180 degrees). It will take a small amount of coolant every few minutes but I still have at least a gallon to go based on what I drained out. Any idea what the noise was? I have seen no leaks from the car since the incident early on.