A troca de óleo e o balanceamento custam pouco.

Because the subject has two items: a troca de óleo and o balanceamento.

In Portuguese, when two nouns are joined by e (and), the verb normally goes in the plural:

• A troca de óleo custa pouco. = The oil change costs little.
• O balanceamento custa pouco. = The balancing costs little.
• A troca de óleo e o balanceamento custam pouco. = The oil change and the balancing cost little.

So custam agrees with both things together.

Because troca is a feminine noun, while balanceamento is a masculine noun.

So their definite articles are different:

• a troca
• o balanceamento

This is just grammatical gender. It does not mean the things themselves are literally feminine or masculine.

Repeating the article is the most natural and standard way here because these are two separate services:

• a troca de óleo
• o balanceamento

So A troca de óleo e o balanceamento clearly means the oil change and the balancing.

If you leave out the second article, the sentence may sound more compressed or less natural in normal speech. In some contexts, especially informal lists or headlines, Portuguese may omit repeated articles, but in a full sentence like this, repeating o sounds better.

Because troca de óleo is a fixed way to describe the type of service: oil change.

Here, de óleo means something like of oil or oil-related, without pointing to a specific oil. Portuguese often uses de + noun with no article to name categories or types:

• troca de óleo = oil change
• filtro de ar = air filter
• posto de gasolina = gas station

If you said do óleo, that would mean of the oil or for the oil, referring to a specific oil already known from context.

In this context, it refers to wheel balancing as a car service.

On its own, balanceamento can mean balancing in a general sense, but with car-maintenance vocabulary, it usually means balancing the wheels/tires. Portuguese often uses the service noun by itself when the context is obvious.

Here, pouco is working adverbially with custam, so it means little:

• custam pouco = cost little

It is not describing the nouns directly, so it does not change for gender or number here.

Compare:

• custam pouco = they cost little
• são baratos = they are cheap

Both can express a similar idea, but the structure is different:

• pouco modifies the verb custar
• baratos is an adjective agreeing with the plural subject

Yes, often that is a very natural English translation in context.

Literally, custam pouco means cost little, but depending on the situation, English may prefer:

• The oil change and wheel balancing are cheap
• ...don’t cost much
• ...are inexpensive

So the literal structure and the best natural translation are not always exactly the same.

It is singular.

Even though an oil change may involve several steps, the whole service is treated as one thing:

• a troca de óleo = the oil change

If you were talking about several oil changes, then you would use the plural:

• as trocas de óleo

The same logic applies to o balanceamento / os balanceamentos, although in real life the singular is much more common for a single service.

In standard Portuguese, no. With a compound subject joined by e, the normal form is plural:

• A troca de óleo e o balanceamento custam pouco.

Using custa would sound ungrammatical to most speakers in this sentence.

The accent mark shows the stressed syllable and the vowel quality.

óleo is pronounced with stress on the first syllable: Ó-le-o.

The accent on ó helps show that pronunciation. It also distinguishes the correct stress pattern from what a learner might otherwise guess.

With the definite articles a and o, Portuguese often sounds more definite than English even when making a general statement.

So this sentence can naturally mean something like:

• Oil changes and wheel balancing are inexpensive
• The oil change and the wheel balancing don’t cost much

Portuguese uses definite articles more often than English, so you should not always translate them word-for-word as the in a strict sense.

Yes, absolutely. Troca de óleo is a very common everyday expression in Brazil for an oil change.

It is the normal term you would hear at a garage, service station, or auto shop. So this is practical, natural vocabulary.