Following a recent water pump replacement on my 1998 Dodge Durango, I have been losing considerable coolant (overheat temperature and warning light comes on). I see no coolant leak at all under hood or on the ground.
This condition keeps happening after approximately 150 miles of driving. Shop says all seems normal including the water pump, hoses etc.
If coolant isn't steaming out from under the hood or dripping on the floor of your garage, it's either coming out the tailpipe as vapor or going into the engine's crankcase -- almost always out the tailpipe.
It's most likely a bad head gasket or cracked cylinder head allowing coolant into the combustion chamber, where it's burned up and emitted through the exhaust. On rare occasions a crack in the engine block can pass coolant into the crankcase. But that's a tough one to miss. The engine oil would look like Pepto-Bismol.
Testing involves pressurizing each cylinder one-by-one, and checking to see if the compressed air comes gurgling up in the radiator. Once the leaking cylinder is confirmed, the affected cylinder head comes off for a visual inspection. The head should then be checked for warpage or cracks. A warped head can be corrected by machining, but cracks require replacement.
Another rare one is a crack between the engine block's cylinder wall and a coolant galley, which would also burn coolant. But I'd put money on the head gasket.