If properly maintained, cars remain operational for several years.
If properly maintained, cars will remain operational for several years
What difference to the meaning of the sentence does using will make?
tl;dr - very little difference, if any; it's more a matter of style.
will modal verb 1 Expressing the future tense. ‘you will regret it when you are older’ 2 Expressing inevitable events. ‘accidents will happen’ - ODO
There are two ways it could be argued that the addition of will changes the sense of the original sentence:
In practice, though, the simple present "remain" can already be considered forward-looking. One could argue that the original can be considered to be a statement expressing a timeless truth, so it can be applied to past maintenance. However, to the extent that holds, the second version (with will) can also be considered a 'timeless' statement, also applicable to past maintenance.
There is some justification for asserting that will emphasises the assertion. However, the if-then structure already qualifies the assertion, making the will-emphasis somewhat redundant.
The addition of the word will is mostly stylistic, adding very little to the meaning of the sentence.