A crack will not always show up until the engine is up to temp, then the leak will be evident. After the engine cools down the leak is all but nonexistent.
Do the compression and pressure tests w/the engine hot.
When you do the compression test (hot or cold), set the parking brake, block the wheels, disconnect the ignition. Then block the throttle wide open and crank the engine over- only let the gage "pump" three times- don't keep cranking until the gage quits rising. You need to be able to see the gage as you crank the engine.
You can have only one cylinder that pumps bad if the leak is between a cylinder and a water jacket.
When you do the cooling system pressure check, if you can, get the engine up to operating temp. w/o the cap on the radiator. Shut the engine off and pressurize the cooling system, then remove the plugs.
Keep the system pressurized until the engine has cooled off, then crank it over to see what cylinder the water comes out of.
If you choose to keep the cap on while the engine is warmed up, carefully remove the radiator cap by using the "first click" position to relieve the pressure if you don't have a pressure relief lever on the cap.