If your losing coolant try this with engine hot. You may need to loosen the spark plugs first (cold engine) so they can be removed for the test without harming the threads/head. With the cooling system hot and pressurized with radiator cap on, spark plugs out, have someone spin the engine over while you watch for mist and/or steam being blown out of the spark plug holes. If none you’re ok. If you see some mist and/or steam you probably have a cracked head or bad head gasket. Is your front windshield fogging? If so could be heater core…
Edit: sorry. It’s a boat engine. I personally think what you’ve described is ok. That much lose could be your pressure tester. Either way, good to go.