Well I hope it's fine, but what I was meaning that your cooling system may have only 16 psi, but your compression is like 250 psi. Coolant may not get into the cylinder, but compression gases may enter the cooling system causing it to get hot and putting an air pocket in the cooling system that may lead to coolant loss and/or overheating. There is no way to pressurize the cooling system enough to force coolant into the cylinder, but the other way of getting compression gases into the cooling system is measurable with a simple radiator hydrocarbon leak checker. It's a simple dye used in a clear glass tube placed on top of the radiator where the cap normally goes. You start the engine and watch the fluid in the container. In the presence of hydrocarbons, the fluid goes from dark blue to bright yellow/green. If it doesn't change colors, you are good to check else where for issues like waterpump flow, thermostat operation, etc.

Greg