O óleo do motor está baixo.

Do is the contraction of de + o.

• de = of
• o = the
• do = of the

So óleo do motor literally means oil of the engine.

Portuguese often uses this de + noun structure where English might use a noun as an adjective:

• engine oil → óleo do motor
• car door → porta do carro
• house roof → telhado da casa

You could theoretically separate it as de o, but in normal Portuguese it contracts to do.

Portuguese has two main verbs for to be: ser and estar.

Here, está is used because the sentence describes a current condition or state: the oil level is low right now.

• é is usually for identity, permanent characteristics, definitions, and general facts.
• está is for temporary states, conditions, location, and situations.

So:

• O óleo do motor está baixo. = The engine oil is low.
• Using é baixo here would sound wrong, because the sentence is not describing the oil as inherently a low thing.

Because baixo agrees with óleo, and óleo is a masculine singular noun.

Agreement in Portuguese usually works like this:

• masculine singular → baixo
• feminine singular → baixa
• masculine plural → baixos
• feminine plural → baixas

Here:

• o óleo = masculine singular
• so the adjective is baixo

Example comparison:

• A temperatura está baixa.
• O nível está baixo.

Here it means low in level/amount.

Even though baixo often literally means low in a physical sense, it is also commonly used for levels, quantities, readings, and measurements.

So in this sentence it refers to the oil level being below what it should be.

Similar uses:

• A pressão está baixa. = The pressure is low.
• A bateria está baixa. = The battery is low.
• O nível da água está baixo. = The water level is low.

Yes, it is understandable and natural enough, especially in everyday speech.

That said, a more explicit version is often:

• O nível do óleo do motor está baixo.

This is a bit more precise because what is really low is the level of the oil, not the oil itself.

In casual speech, though, people often shorten things when the meaning is obvious from context, so O óleo do motor está baixo works.

Portuguese uses definite articles more often than English.

So where English might simply say Engine oil is low or The engine oil is low, Portuguese naturally says:

• O óleo do motor está baixo.

The article o marks óleo as a specific thing being discussed: the oil in that engine.

Using no article here would sound unnatural in standard Portuguese.

Óleo is pronounced roughly like OH-lyoo, with the stress on the first syllable.

A helpful breakdown:

• ó = stressed o
• leo is pronounced smoothly, almost like lyoo

In IPA, Brazilian Portuguese pronunciation is approximately /ˈɔ.le.u/, though in natural speech the middle and final vowels may flow together a bit.

The written accent in ó tells you that the stress goes there.

The accent in está shows the stressed syllable: es-TÁ.

It also helps distinguish forms in writing. In practice, the accent tells you this word is pronounced with stress on the last syllable.

So:

• está → es-TÁ

This is the third-person singular form of estar:

• eu estou
• você/ele/ela está
• nós estamos

In this sentence, está agrees with o óleo, which is singular.

No, that would not be the normal or correct choice here.

Use está baixo, not é baixo, because you are talking about the oil’s current level or condition.

A quick rule of thumb:

• ser = what something is
• estar = how something is

Here, the sentence means the oil level is currently low, so estar is the right verb.

Yes. Some common alternatives are:

• O nível do óleo do motor está baixo.
  More precise and very natural.

• O motor está com pouco óleo.
  Literally, The engine has little oil. Very common in speech.

• Está faltando óleo no motor.
  Literally, Oil is lacking in the engine.

• O óleo está baixo.
  Possible if the context already makes it clear you mean the engine oil.

These all express a similar idea, but the original sentence is perfectly understandable.

Yes, very close.

Portuguese usually prefers de structures where English might use either:

• a possessive: the engine’s oil
• or a noun modifier: engine oil

So:

• óleo do motor = the engine’s oil / engine oil

Portuguese generally does not stack nouns the way English does. Instead of motor oil as two nouns side by side, Portuguese normally says óleo de motor or óleo do motor, depending on the meaning.

A useful distinction:

• óleo de motor = motor oil, engine oil in a general sense
• óleo do motor = the oil of the engine, the specific engine’s oil

This is a very useful distinction.

• óleo de motor means motor oil / engine oil as a type of product.
• óleo do motor means the oil of the engine, referring to a specific engine’s oil.

So:

• Preciso comprar óleo de motor.
  I need to buy motor oil.

• O óleo do motor está baixo.
  The engine oil is low.

In the sentence you gave, do motor is the natural choice because it refers to the oil in a particular engine.

Here, baixo is an adjective functioning like a description after the verb estar.

The structure is:

• O óleo do motor = subject
• está = verb
• baixo = adjective describing the subject’s condition

This is similar to:

• A porta está aberta. = The door is open.
• A luz está acesa. = The light is on.
• O tanque está vazio. = The tank is empty.

So baixo is describing the current state of the oil level.