help...no heat

[MarineOne]

So tell me where I'm confused. When the thermostat opens up, I'll actually be losing heat that could otherwise be routed into my car? I thought that it was vice versa; when the 'coolant' got warm enough for it to open it, I would be able to 'flow it' through my vents into the car. So in other words, I really don't need to see if the thermostat is opening because if it's not then I shouldn't be losing heat anyway? I was pretty sure it was the opposite of that; that if it wasn't opening, I wasn't going to get warm air...