Why is the upper radiator hose hot while the lower one is not?

[AngelaMarie]

When the upper radiator hose is hot while the lower one is not, it indicates a malfunctioning thermostat. Here are some relevant details about engines: 1. Energy Conversion: An engine is a machine that converts other forms of energy into mechanical energy, including internal combustion engines (reciprocating piston engines), external combustion engines (Stirling engines, steam engines, etc.), jet engines, and electric motors. For example, internal combustion engines typically convert chemical energy into mechanical energy. 2. Mechanism: The term 'engine' can refer to either the power generation device itself or the entire machine including the power unit (e.g., gasoline engines, aircraft engines). Engines were first developed in the UK, hence the concept originates from English, with its original meaning referring to 'mechanical devices that generate power.'