Question about pressure and level in coolant

[blue62]

Originally Posted by KuaiThunder

Thx for the reply.

I changed both the cap and bleed valve few months back when I have moisture issue which solved the moisture problem.

I can understand the pressure build up in the system but I can't understand why pressure pushed down the coolant level. I suppose coolant is not compressible so it has to go some where. I am thinking maybe I have a fail thermostat so the pressure pushed the valve open.

Full is full and liquid is not compressible so I don't think thermostat open or closed or failed would be the issue.
Sounds like you have air trapped in the system or older coolant hoses that are expanding as pressure in the system rises.