The most common and most likely answer to this crossword clue is the 3 plus 4 letter word TOW ROPE
I've seen this crossword clue in The Guardian
T
O
W
R
O
P
E
More clues leading to the result TOW ROPE
Buddy explains!

The straight part
We know that "What may help car" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what may help car = tow rope.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.