The result of an internal combustion engine is the transformation of heat energy into kinetic energy. Thermodynamics says this conversion cannot be 100%. Hence some of the heat is not converted. The "wasted" heat is not lost. It is simply not used.

To say the purpose of an internal combustion engine is not to use heat energy distorts the meaning of the words to the vanishing point by implying that the purpose of everything is not to use heat to the degree they don't do it.

The statement is "what it does". Its not "what it doesn't do".