I changed my Temperature Sender Unit (for Dash Gauge) which is located in the Regulator Housing (Thermostat housing) on my C13.
I thought it odd that no coolant came out when I pulled the Sender Unit out. I was prepared to do a fast swap.
After looking/thinking about it, I see that the coolant level in the engine is below the Regulator housing when the engine is shut off.
The way the Surge tank is mounted, the cold fill line for the Surge Tank is below the engine upper hose and regulator housing - and the top of radiator is below the top of engine - so there is no coolant in the upper radiator hose. I could add more coolant to the surge tank (near max line) to have coolant in the Regulator housing (and then Sender Unit would be submerged) when engines is off.
I guess it's not a problem as my engine does not overheat.
Is this typical on Beavers (motor coaches)? Now that I think about it, I don't recall ever seeing any cars or trucks with the radiator or surge tank lower than the top of engine.