Originally Posted by Extinct

You can perform this test yourself, Advanced Auto Parts has a cooling system pressure test kit that you can rent/borrow. Start the test with the engine cold and off, pump it up to about 20 or 25 psi and it should hold pressure overnight. Once it is up to pressure if there are any external leaks you should be able to hear them or see them. If it does not hold pressure and there are no external leaks that means it is leaking internally. You can get a borescope off of Amazon for about $20 and check each cylinder through the spark plug hole to see if any coolant has leaked into the cylinder from the pressure test. Best to do the test with the spark plug out of cylinder 7 and 8 and then turn it over by just momentarily bumping the starter so that it moves very slowly and expels any coolant that has accumulated in the cylinder through the spark plug hole. People with major leaks have been connecting rods by filling the cylinder with coolant and then hitting the starter. Some of our Northeast contributors should be able to comment but to my knowledge Atlantic British, JE Robison, and TWS are not too far from you.