It's pretty much like a lesser car, except the thermostat has a slit o-ring gasket seal around it. It probably does not come with the t-stat, so you'll need to order separately. (If someone replaced it already but left the gasket seal out, that would cause what you are seeing.) Also, pay attention to the t-stat orientation, as some have bleed holes to let the air out. If it's not oriented right, it's really hard to get the system filled back up.

Gerry