Why is your upper heater hose collapsing?

The upper heater hose may be collapsing due to a combination of factors, primarily related to vacuum issues or internal blockages. If the engine is not properly venting, it can create a vacuum that pulls the hose inward. Additionally, a buildup of debris or a failing thermostat can restrict coolant flow, leading to pressure imbalances that cause the hose to collapse. Inspecting for blockages and ensuring the cooling system is functioning correctly can help resolve the issue.