Antes de salir, mi madre miró si había suficiente gasolina para llegar a la playa.

In Spanish, antes is normally followed by de when the next verb is in the infinitive.

• antes de salir = before leaving / before going out
• después de comer = after eating

So de is required here. Saying antes salir would sound ungrammatical.

Because after antes de, Spanish uses the infinitive when the subject is the same or when the action is being referred to in a general way.

• Antes de salir, mi madre... = Before leaving, my mother...

It works like English before leaving. Spanish often uses antes de + infinitive where English may use either before leaving or before she left, depending on style.

It could be understood as either, depending on context. Salir has a broad meaning:

• to go out
• to leave
• to head out

In this sentence, it most naturally means something like before leaving / before setting off.

Spanish often states the subject noun directly and usually does not need a subject pronoun if the verb already makes the subject clear.

• mi madre miró... = my mother checked...

Using ella would only be necessary for emphasis, contrast, or clarity.

Also, mi madre is a neutral, standard way to say my mother. Mamá is more personal and familiar.

Miró is the preterite, which is used for a completed action in the past.

Here, the mother performed one specific action:

• she checked the fuel once, before leaving

So:

• miró = checked / looked
• miraba would suggest an ongoing, repeated, or background action, which does not fit as well here

This sentence describes a finished event, so miró is the natural choice.

Yes, mirar literally means to look, but in context it can also mean to check or to see.

So mi madre miró si había... means:

• my mother checked whether there was...

This is a common extension of mirar in everyday Spanish:

• Mira si está abierto. = Check if it’s open.
• Voy a mirar el horario. = I’m going to check the timetable.

Here si means whether / if in an indirect question.

• miró si había suficiente gasolina = she checked whether there was enough petrol

This is not a conditional if. It introduces the thing being checked.

Very common pattern:

• No sé si viene. = I don’t know whether he’s coming.
• Preguntó si estaba listo. = He asked whether it was ready.

Because haber is used to mean there is / there are / there was / there were.

• había suficiente gasolina = there was enough petrol

You cannot use estar for simple existence in this way.

Compare:

• Había gasolina. = There was petrol.
• La gasolina estaba en el garaje. = The petrol was in the garage.

So haber is for existence; estar is for location or state.

Both are past forms of haber, but they are used differently.

• había is the imperfect
• hubo is the preterite

In this sentence, había suficiente gasolina describes a situation or state that existed at that moment, not a sudden event. That is why había sounds natural.

• miró si había suficiente gasolina = she checked whether there was enough petrol

Hubo suficiente gasolina would sound more like there ended up being enough petrol or there was enough petrol as an event, which is not the idea here.

Suficiente does not change to suficienta. It has the same form for masculine and feminine singular.

• suficiente gasolina
• suficiente agua
• suficiente tiempo

In plural, it becomes suficientes:

• suficientes litros

Also, suficiente usually goes before the noun in this kind of sentence:

• suficiente gasolina = enough petrol

You may sometimes see gasolina suficiente, but suficiente gasolina is the more natural order here.

Because gasolina is an uncountable noun here, like petrol or gasoline in English.

You normally talk about it as a substance, not as separate countable units:

• hay gasolina
• no había suficiente gasolina

If you want to count it, you would need a unit:

• dos litros de gasolina
• suficientes litros de gasolina

Para + infinitive is used to express purpose or goal.

• para llegar a la playa = to get to the beach / in order to reach the beach

It explains what the petrol is needed for.

This is a very common structure:

• Estudio para aprender. = I study to learn.
• Trajo agua para beber. = He brought water to drink.

Because llegar normally takes the preposition a before a destination.

• llegar a casa
• llegar al hotel
• llegar a la playa

So:

• para llegar a la playa = to get to the beach

The a is part of the verb pattern.

Both are possible, but they do not mean exactly the same thing.

• suficiente gasolina = enough petrol in a general sense
• la suficiente gasolina = the necessary/required amount of petrol, often more specific or emphatic

In this sentence, the more neutral and natural wording is había suficiente gasolina.

Yes, but the structure is different.

• Antes de salir = Before leaving
• Antes de que saliera = Before she left / before he left

Antes de + infinitive is used when Spanish can leave the subject more general or understood.

Antes de que + subjunctive is used when the clause has its own explicit subject or when you want a full subordinate clause.

So in this sentence, antes de salir is shorter and very natural.

Yes. In Spain, gasolina is the standard word for petrol/gasoline.

Depending on the Spanish-speaking country, other terms may also appear, but for Spain this is the expected word.

The sentence breaks down like this:

• Antes de salir = time expression: before leaving
• mi madre = subject: my mother
• miró = main verb: checked
• si había suficiente gasolina = indirect question: whether there was enough petrol
• para llegar a la playa = purpose/result idea: to get to the beach

So the pattern is:

Before leaving, my mother checked whether there was enough petrol to get to the beach.

This is a very common Spanish structure:
time expression + subject + past verb + si-clause + para + infinitive