Following a recent water pump replacement, I have been losing a considerable amount of coolant (engine heats to over heat temp and warning light comes on). I see no coolant leak at all under the hood or on the ground? This condition keeps happening after approximately 150 miles of driving. Shop says all seems normal-water pump, hoses etc. What can be the cause/cure?
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.