Why does a car's engine get hot?

Why does a car's engine get hot when it is running?

A car's engine is not efficient.

The engine works by converting chemical energy in the form of fuel to the mechanical energy (work) that drives the wheels and makes the car move. But only about 20 to 30 percent of the chemical energy is actually converted to mechanical energy. What happens to the remaining 70 to 80%?

It gets converted to heat.

In fact, thermodynamics tells us that we cannot convert the fuel completely into work. This is the result of the famous Second Law of Thermodynamics.

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