Learn Spanish (Latin America): El mecánico tuvo que volver a cambiar el aceite. - The mechanic had to change the oil again.

The phrase volver a followed by an infinitive (like cambiar) is a very common way in Spanish to express doing something again. Instead of adding a separate word for "again" at the end of the sentence, Spanish builds it right into the verb chain. It essentially translates to "to return to change."

Why are both volver and cambiar in their infinitive forms?

When you chain verbs together, only the first working verb is conjugated. Here, tener is conjugated in the past tense as tuvo to match the mechanic. The following verbs stay in their dictionary form (infinitive) and are just connected by their required prepositions: tener que + volver a + cambiar.

Could I say El mecánico tuvo que cambiar el aceite otra vez instead?

Yes, using otra vez or de nuevo at the end of the sentence is perfectly correct and means the same thing. However, using the volver a structure is extremely common in everyday speech, so mastering it will make your Spanish sound much more native.

Why use the preterite tuvo instead of the imperfect tenía here?