I think the translation would become "I was always using dad's car", but the sentence is "I always used dad's car", which to me implies that I no longer use dad's car, in which case the preterite is correct.
By saying “I always used” you are saying this was an ongoing action in the past which is the definition of the imperfect tense. If you used the car in the past, but continue to use it you would say “I’ve always used dad’s car.” To really be the preterite, omit the word “always/siempre.”
An ongoing action hints strongly at an imperfective aspect, but it's neither a requirement nor its definition. The crucial part is whether you treat the whole action you're talking about as a single, finalised point in time (perfective), or if you treat it as an event with a duration, witnessing it from within (imperfective).
For instance if you say "I always used dad's car as long as he had it", you're using a perfective aspect. You're establishing a clear timeframe, and you don't give the action a meaningful duration. It just happened in the past and then it was over. Nothing else happened during it.
If you intend to make an accurate translation, NO.
"Dad" is "papá", "daddy" is "papito" and "father" is "padre".
So "I always used father's car" would be (in a very old fashioned Spanish because nowadays almost no one refers to his father like that) would be "Siempre usé el coche de padre"
Let me remember also that "CARRO" is only used in Southamerica for "CAR". In Spain a "carro" is used for "CART" like in "A horse cart". We in spain say "auto" or "coche".
Are you claiming father and papa don't mean the same thing? You are making up these direct translations. "papa" and "padre" both mean ones father despite the way you feel they should be translated.
The terms refer to the same person (mostly), but they are still different terms. Padre is formal and papá is affectionate.
In English, "Dad" should be capitalized when it is used in place of/as a name, just as you would capitalize "Sara" if the sentence read "I always used Sara's car." If the sentence read, "I always used my dad's car," then "dad" would not need capitalization.
In Spanish ALL the information is INSIDE the verb. (Person, number and tense). Not as easy to remember as English tenses, but richer and more plastic to build sentences. Also sometimes in some cases it leads to confusion.
usé is the first person singular preterite (past tense) conjugation of the verb usar - to use. there are good references for conjugating the -ar, -er & -ir regular verbs online. just google Spanish verb conjugations.
Uso is one of the given options. Yo siempre uso, I always use, would that not work?