My '01 Expedition intermittently blows cold air. Thermostat replaced. on 2001 Ford Expedition

Feels like no pressure in hose. Shut vehicle off, let cool for few minutes...restart and will run fine. Any help what could be the problem?

Asked by for the 2001 Ford Expedition
Suspect there may be an air pocket restricting coolant flow. You might want to have it tested for exhaust gasses in the cooling system.