The Oxford Learner's Dictionary gives the following definitions for "will":
Definition 7) used for stating what is generally true.
a) Engines won't run without lubricants.
What is the difference between sentence a) and sentence b) of mine? Is a) less confident than b)?
b) Engines don't run without lubricants.
Definition 8) used for stating what is true or possible in a particular case.
c) This jar will hold a kilo.
What is the difference between sentence c) and sentence d) of mine? Is c) less confident than d)?
d) This jar holds a kilo.