Coolant level on closed loop system

[bobweiser]

Should the coolant level change on the closed loop system once warm versus cold?

[Eagle]

Yes.

 

When cold, the bottle should be half full. At operating temperature, the coolant expands, which is what creates the pressure. At operating temperature there should be almost no air space in the surge bottle.

[bobweiser]

So if it doesn't get full, is this due to lack of pressure or bad thermostat? According the my newly installed used guage cluster, the truck is running at 240 yet my temp gun doesn't indicate that. I feel flow and get heat in the cab. Just trying to understand this system.