What issue can be caused by a restricted heater return hose?

A restricted heater return hose can lead to excess heat in the passenger compartment because it impedes the circulation of coolant back to the engine. When the return hose is restricted, it can create a backup of coolant in the heater core, leading to a buildup of heat in the passenger area since the heated coolant remains trapped in the heater core longer than intended. This not only results in a warmer cabin than desired but can also make it challenging to regulate the temperature effectively.

Additionally, the restriction may prevent the system from utilizing the full potential of heater operation, as the hot coolant is not effectively cycled back to the engine to complete the heat exchange process. This problem could also exacerbate other issues in the cooling system, contributing to potential overheating problems for the engine itself. The cabin comfort could be compromised, leading to a less enjoyable driving experience.